Optical storage medium, optical read/write apparatus, and optical read/write method

ABSTRACT

An optical read/write apparatus causes a read/write light beam from illuminating means to strike only one side of an optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers. In this case, the optical read/write apparatus operates so that data is read/written from/into a second data storage layer after fully recording a recordable area of a first data storage layer. Thus, light can be shone with uniform intensity across the substantially entire recordable area of the second data storage layer without using a complex read/write system even under such conditions that the transmittance to light of the first data storage layer in the recordable area may vary depending on whether any data is recorded in the recordable area.

This is a divisional patent application of co-pending U.S. patentapplication Ser. No. 10/142,488 filed 10 May 2002, by Junji Hirokane andNoboru Iwata, the same inventors as of this divisional application,entitled—OPTICAL STORAGE MEDIUM, OPTICAL READ/WRITE APPARATUS, ANDOPTICAL READ/WRITE METHOD.

FIELD OF THE INVENTION

The present invention relates to optical storage media having aplurality of writeable and/or readable data storage layers, opticalread/write apparatus using such media, and optical read/write methodusing such media.

BACKGROUND OF THE INVENTION

Recent years have seen on-going development of optical read/writeapparatus capable of writing a large amount of data, like video data indigital format, and randomly accessing such data. Also, various attemptsare being made to increase the storage density of optical disks used asstorage media in such optical read/write apparatus.

In optical read/write apparatus, attempts are being made to increasestorage density by means of, for example, an increased numericalaperture of an objective lens and the use of short wavelengthillumination for a smaller light beam spot. The efforts have beensuccessful and the storage capacity optical disks are getting largeryear after year. Technology has already established as to a DVD-ROM(Digital Versatile Discs for Read Only Memory) as an optical disk whichnow has doubled its capacity owning to double layer structure.

A document entitled “A 16.8 GB Double-Decker Phase Change Disc”distributed in Joint International Symposium on Optical Memory andOptical Data Storage 1999 discloses an optical disk with an addeddensity thanks to the double data storage layers which are writeable andreadable.

In the optical disk disclosed in the document, each data storage layeris made of phase change material. Such optical disks are classified intotwo types: Low-to-high media which has a higher reflectance in recordingmark areas than in interval areas interposed between recording markareas and high-to-low media which conversely has a higher reflectance ininterval areas than in recording mark areas. Both types of media enablethe readout of data by means of quantities of reflected and transmittedlight which vary depending on whether the phase change material is inpolycrystal or amorphous phase. Similar optical disks using phase changematerial are disclosed in, for example, Japanese Laid-open PatentApplication 2001-52342 (Tokukai 2001-52342, published on Feb. 23, 2001).

However, for example, on the high-to-low medium having a higherreflectance in interval areas than in recording mark areas, mark rowswhich include low reflectance amorphous areas are formed along guidinggrooves in recorded areas. In the optical disk, data is written or readon a first data storage layer close to the light-striking side and on asecond data storage layer far from the light-striking side using lightincident to the same side of the disk, the light beam first travelsthrough the first data storage layer before writing or reading data onthe second data storage layer. Accordingly, upon writing or reading onthe second data storage layer, the intensity of light beam reaching thesecond data storage layer after passing through the first data storagelayer must differ depending on whether or not the first data storagelayer already holds any records, so as to produce different writing orreading power sensitivities with respect to the second data storagelayer.

Therefore, to write or read data on the second data storage layer, thefirst data storage layer must be checked first to determine whetherthere are any records on it, so that the write or read light beamintensity can be specified. This adds complexity to the write/readsystem. A problems arises here that optical writing/reading system usingsuch an optical disk is hardly practicable.

As mentioned above, Japanese Laid-open Patent Application 2001-52342discloses an optical disk having a double data storage layer structurein which address information is provided in the form of wobbling grooveso as to achieve stable writing and readout.

Referring to FIG. 64, an optical disk 501 provided with conventionaldouble data storage layers has a center hole 502 at the center. Data iswritten/read in a recordable area 503 in which a spiral guiding grooveis provided for data write and readout.

The optical disk 501 has an address area 504 occupying a certain angularpart. Address information is stored in the address area 504 as addresspit rows extending radially. Throughout this text, this configuration,in which address information is stored collectively in one place, i.e.,the address area 504 in the case of the optical disk 501, will bereferred to as a lumped address scheme.

FIG. 65 shows the optical disk 501 in vertical cross section. Theoptical disk substrate 506 has thereon a guiding-groove-formed layer 507on whose surface a spiral guiding groove is formed from depressions andprojections, a second storage layer 508, a guiding-groove-formedintermediate layer 509, a first storage layer 510, surface-coating layer511 which are deposited in the order. To write/read data on the firststorage layer 510 and the second storage layer 508 in the optical disk501, a focused light beam 512 is shone onto the first and second storagelayers 510, 508 via only one side of the disk, that is, the side of thesurface-coating layer 511.

FIG. 66 shows an enlarged view of a guiding groove 513 and a part ofaddress pit rows 515 in the address area 504. On the optical disk 501,recording marks 1114 are formed along the spiral guiding groove 513, andthe address pit rows 515 are formed extending from the guiding groove513 in the address area 504.

To read/write data on the first storage layer 510 in the optical disk501, as shown in FIG. 67, the light beam 512 to focused to illuminatethe first storage layer 510 by means of tracking along the guidinggroove 513 on the first storage layer 510 while controlling theintensity of the light beam. To read/write data on the second storagelayer 508, the light beam 512 is focused to illuminate the secondstorage layer 508 by means of tracking along the guiding groove 513 onthe second storage layer 508 while controlling the intensity of thelight beam.

Under these conditions, let us suppose that the optical disk 501 is aphase change storage medium of a high-to-low type in which, for example,interval areas have high reflectance, i.e., lower transmittance, thanthe recording marks 1114 on the first storage layer 510 and the secondstorage layer 508.

In the event, to read/write data on the second storage layer 508, alight beam 512 d passes through the area where there is the guidinggroove 513 on the first storage layer 510 and is focused onto the secondstorage layer 508, only after having passed through the area where thereexist the recording marks 1114 which have relatively bettertransmittance. In contrast, a light beam 512 d passes through theaddress area 504 of the first storage layer 510 and is focused onto thesecond storage layer 508, only after having passed through the areawhere there are no recording marks 1114 which have higher transmittance,that is, a low transmittance area. Therefore, the intensity of the lightbeam 512 e having passed through the area where there is the guidinggroove 513 on the first storage layer 510 becomes greater than that ofthe light beam 512 d having passed through the address area of the firststorage layer 510.

Therefore, referring back to FIG. 66, as to the optical disk 501 havingaddress area where address pit rows 515 are lumped together, theintensity of a light beam focused onto the second storage layer 508varies between the address area 504 and the other area where the guidinggroove 513 is provided. This makes it impossible perform stablewrite/readout.

To solve these problems, in the aforementioned prior art patentpublication, no address area 504 with address pit rows 515 in FIG. 66 isprovided. Instead, it suggests that the variations in intensity of thelight beam focused on the second storage layer 508 be restrained byproviding a wobbling guiding groove to record address information in theform of wobbles. Throughout this text, the configuration, in whichaddress information is not stored collectively in one place, butdistributed will be referred to as a distributed address scheme.

However, in the configuration disclosed in the prior art patentpublication, address information is stored on the guiding groove in theform of its wobbles. Therefore, the guiding groove needs be scanned overa relatively long period of time to retrieve a single set of addressinformation.

Specifically, each address pit in the address pit rows 515 in FIG. 66has a diameter which is more or less equal to the width of the guidinggroove 513: typically, 0.3 microns to 0.5 microns, and each set ofaddress information is recorded over about 1 mm or less of the guidinggroove 513 in the address area 504.

In contrast, in the case of wobbling guiding grooves, to ensure that thequantity of reflected light does not vary in tracking, each wobble mustbe several tens of microns long, that is, each address area storing aset of address information must be about 100 mm long in a wobblingguiding groove.

In a lumped address scheme using address pit rows 515, addressinformation is completely reproduced when about 1 mm or less of theaddress area is scanned. Meanwhile, in a distributed address schemeusing a wobbling guiding groove, address information is completelyreproduced only when about 100 mm of the guiding groove is scanned,which is relatively long. Distributed address scheme is therefore not toachieve high speed randomly access in optically reading/writing data onoptical disks. Lumped address scheme should hence be employed toreproduce address information instantly.

Now referring to FIG. 68, another conventional optical disk 601 has acenter hole 602, a recordable area 603, innermost part 604, an outermostpart 605, and prepit areas 606.

The optical disk 601 is provided with a guiding groove (not shown) whichis, for example, spiral. Tracking is done along the guiding groove toread/write data in the recordable areas 603 by shining a light beam 621onto first and second storage layers (double layers) 611, 612 as shownin FIG. 69. In the prepit areas 606, or the inner prepit area 606 a andouter prepit area 606 b, of the first and second storage layer 611, 612,are there formed pit rows (not shown) which form, for example, a spiral.Tracking is done along the pit rows, and a light beam 621 is shone toreproduce prerecorded information from the pit rows.

FIG. 70 shows an enlarged view around the border between the recordablearea 603 and a prepit area 606. FIG. 71 shows its cross section in whichonly the first storage layer 611 and the second storage layer 612 aredepicted. The following description assumes that the first and secondstorage layers 611, 612 are formed in a phase change storage medium of alow-to-high type whose transmittance is higher in produced recordingmarks than in non-recorded areas.

As shown in FIG. 70 and FIG. 71, if the first storage layer 611, locatedon the light-striking side, has a prepit area 606, light beams 621 a,621 b are focused and shone onto the second storage layer 612 afterrecording marks M are formed along the guiding groove G in therecordable area 603 of the first storage layer 611. In this case,intensity differs between the light beam 621 a, which is transmittedthrough the recordable area 603 and then focused, and the light beam 621b, which is transmitted through the prepit area 606 and then focused.

In the recordable area 603 do there exist multiple recording marks Mwith high transmittance, and the light beam 621 a transmitted throughthe recordable area 603 of the first storage layer 611 has a relativelyhigh intensity. In the prepit area 606 do there exist no recording marksM, and the light beam 621 b transmitted through the prepit area 606 ofthe first storage layer 611 has a relatively low intensity. As could beunderstood from this, the provision of a prepit area 606 in the firststorage layer 611 causes undesirable variations in reading/writing powerin reading/writing and makes it impossible to read/write data on thesecond storage layer 612 in a stable manner.

SUMMARY OF THE INVENTION

The present invention has an objective to offer an optical storagemedium, an optical read/write apparatus, and an optical read/writemethod, with which light can be shone with uniform intensity across thesubstantially entire recordable area of the second data storage layerwithout using a complex read/write system even under such conditionsthat the transmittance to light of the first data storage layer in therecordable area may vary depending on whether any data is recorded inthe recordable area.

In order to achieve the foregoing object, an optical storage medium ofthe present invention includes stacked data storage layers each of whichis readable/writeable separately from the other layers by means of onlya light beam striking one side of the optical storage medium, and ischaracterized in that a recordable area of a first data storage layerhas adjacent to an end thereof an extended area covering more than anarea directly above a recordable area of a second data storage layer ina direction in which the first and second data storage layers arestacked, the first data storage layer being one of the data storagelayers which is located closest to a light-striking surface of themedium, the second data storage layer being another of the data storagelayers which is located next to the first data storage layer, oppositethe light-striking surface.

According to the arrangement, the recordable area of the first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked. Therefore, if data is read/written from/in therecordable area of the second data storage layer after fully recordingthe recordable area of the first data storage layer, substantially allthe read/write light striking the second data storage layer afterpassing through the first data storage layer passes through the recordedrecordable area of the first data storage layer upon reading/writing onthe second data storage layer.

Therefore, light can be projected at uniform intensity on substantiallyall recordable areas of the second data storage layer even when theoptical transmittance of the recordable area of the first data storagelayer varies depending whether the recordable area is fully recorded ornot. Therefore, desirable read/write characteristics can be impartedwithout using a complex read/write system.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium, and is characterized in that the apparatusincludes controlling means for controlling the illuminating means sothat the extended area of the optical storage medium is fully recordedbefore a recordable area of the first data storage layer of the opticalstorage medium is recorded except for the extended area.

An optical read/write method of the present invention includes the stepof fully recording the extended area before recording a recordable areaof the first data storage layer of the optical storage medium except forthe extended area.

According to the arrangement, since the optical storage medium has anextended area in the recordable area of the first data storage layer,light can be projected at uniform intensity on substantially allrecordable areas of the second data storage layer. Therefore, desirableread/write characteristics can be imparted without using a complexread/write system.

The part of the recordable area of the first data storage layer otherthan the extended area is as large as the recordable area of the seconddata storage layer. The illuminating means is controllable in terms ofits position relative to the optical storage medium in the same mannerin reading/writing in the part of the recordable area of the first datastorage layer other than the extended area and the recordable area ofthe second data storage layer.

Another object of the present invention is to provide an optical storagemedium, an optical read/write apparatus, and an optical read/writemethod, with which a desirable reading/writing property can be realizedin an arrangement, using a lumped address scheme, which includes datastorage layers.

In order to achieve the foregoing object, an optical storage medium ofthe present invention includes stacked data storage layers each of whichis readable/writeable separately from the other layers by means of onlya light beam striking one side of the optical storage medium, and eachof the data storage layers has at least one address area where there arecollectively formed address information portions representing addressinformation, and the optical storage medium exhibits an opticaltransmittance which varies when data is written by means of the lightbeam, wherein the address area of a first data storage layer includes arecorded area exhibiting a varied transmittance and a non-recorded areaexhibiting an original transmittance, and the first data storage layeris one of the data storage layers which is located closest to alight-striking surface of the medium, and a second data storage layer isanother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium including stacked data storage layers each ofwhich is readable/writeable separately from the other layers by means ofonly a light beam striking one side of the optical storage medium, andeach of the data storage layers has at least one address area wherethere are collectively formed address information portions representingaddress information, and the optical storage medium exhibits an opticaltransmittance which varies when data is written by means of the lightbeam, and the optical read/write apparatus includes controlling meansfor controlling the illuminating means so that the address area of afirst data storage layer includes a recorded area exhibiting a variedtransmittance and a non-recorded area exhibiting an originaltransmittance, and the first data storage layer is one of the datastorage layers which is located closest to a light-striking surface ofthe medium, and a second data storage layer is another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

An optical read/write method of the present invention includes the stepof causing a read/write light beam to strike only one side of an opticalstorage medium including stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, and each ofthe data storage layers has at least one address area where there arecollectively formed address information portions representing addressinformation, and the optical storage medium exhibits an opticaltransmittance which varies when data is written by means of the lightbeam, wherein the address area in a first data storage layer includes arecorded area exhibiting a varied transmittance and a non-recorded areaexhibiting an original transmittance, and the first data storage layeris one of the data storage layers which is located closest to alight-striking surface of the medium, and a second data storage layer isanother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.

According to the arrangement, upon writing or reading on the second datastorage layer, the intensity of light beam reaching the second datastorage layer after passing through the address area of the first datastorage layer on the light-striking side can be made to be almost thesame as the intensity of a light beam reaching the second data storagelayer after passing through the non-address area in the recordable areaof the first data storage layer. As a result, it is possible toread/write data from/in the second data storage layer steadily anddesirably.

That is, as to the optical storage medium, the non-address area in therecordable area of the first data storage layer has a recorded area, forexample, a recording mark is formed, so that the optical transmittancevaries at the portion. In a case where the address area does not havethe recorded area exhibiting a varied transmittance, upon reading orwriting on the second data storage layer, there is a great differencebetween the intensity of the light beam reaching the second data storagelayer after passing the non-address area and the intensity of the lightbeam reaching the second data storage layer after passing the addressarea.

On the other hand, the present invention is arranged so that the addressarea in the first data storage layer of the optical storage mediumincludes a recorded area exhibiting a varied transmittance and anon-recorded area exhibiting an original transmittance. Thus, also inthe address area, an optical transmittance is varied due to the recordedarea as in the non-address area. Therefore, as described above, theintensity of the light beam reaching the second data storage layer afterpassing through the address area of the first data storage layer on thelight-striking side can be made to be almost the same as the intensityof light beam reaching the second data storage layer after passingthrough the non-address area in the recordable area of the first datastorage layer. As a result, it is possible to read/write data from/inthe second data storage layer steadily and desirably.

According to the optical read/write apparatus or the optical read/writemethod, in a case where the recorded area is formed on the address areain the first data storage layer of the optical storage medium, it ispossible to manufacture the optical storage medium at a lower cost sincethe manufacturing process of the optical storage medium is simplified.

Further, still another object of the present invention is to provide anoptical storage medium, an optical read/write apparatus, and an opticalread/write method, with which data can be read/written steadily withoutbeing influenced by a prepit area. This is realized in an optical dischaving two or more storage layers.

In order to achieve the foregoing object, an optical storage medium ofthe present invention includes: one light-striking-side storage layerprovided as a data storage layer on a light-striking side; and one ormore opposite-side storage layers provided as data storage layersopposite the light-striking side from the light-striking-side storagelayer, wherein, in order to solve the foregoing problems, one of theopposite-side storage layers which is, as a last data storage layer,most distanced from the light-striking-side storage layer has a prepitarea which includes preformed pits representative of data.

According to the arrangement, since the last data storage layer, mostdistanced from the light-striking-side storage layer, has a prepit area,intensity of the striking light is not varied by the prepit area. Thus,it is possible to read/write data from/in the last data storage layersteadily without being influenced by the prepit area.

An optical read/write apparatus of the present invention causes aread/write light beam from an illuminating section to strike only oneside of the optical storage medium, wherein the optical read/writeapparatus includes: the optical read/write apparatus includes: anenvelope detecting section for detecting an envelope of a reproductionsignal obtained from the prepit area; a mean level producing section forproducing a mean level of the detected envelope; and a digitalconverting section for converting the reproduction signal to a digitalsignal using the mean level as a reference.

An optical read/write method of the present invention causes aread/write light beam from an illuminating section to strike only oneside of the optical storage medium, wherein the method further includesthe steps of: producing a mean level of an envelope of a reproductionsignal obtained from the prepit area; and converting the reproductionsignal to a digital signal using the mean level as a reference.

According to the foregoing apparatus and method, an envelope of areproduction signal obtained when the prepit area is reproduced isdetected by the envelope detecting section. Then, the mean levelproducing section produces a mean level of the detected envelope.Thereafter, the digital converting section converts the reproductionsignal to a digital signal using the mean level as a reference. Thus,the mean level is always detected, and the detected mean level is usedas a reference in the digital conversion, so that it is possible toperform the digital conversion without being influenced by variance inamplitude of the reproduction signal. For example, in a case where thereexist a fully recorded portion exhibiting high transmittance afterrecording and an unrecorded portion which holds no record, when a lightbeam that is projected so as to cover the fully recorded portion and theunrecorded portion is focused on the second storage layer, it ispossible to steadily obtain a digital signal from the reproductionsignal even though the reproduction signal strength of prepit datavaries in connection with rotation of the optical storage medium. Thus,it is possible to steadily reproduce the prepit data on the secondstorage layer of the optical storage medium.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view illustrating how anoptical-disk-read/write apparatus of an embodiment of the presentinvention reads/writes data on the second storage layer of an opticaldisk.

FIG. 2 is a plan view of the optical disk shown in FIG. 1.

FIG. 3 is a vertical cross-sectional view showing the structure of theoptical disk shown in FIG. 1.

FIG. 4 is an enlarged vertical cross-sectional view showing a major partof the optical disk shown in FIG. 3 in more detail.

FIG. 5 depicts the structure of an optical-disk-read/write apparatus ofan embodiment of the present invention.

FIG. 6 depicts the optical disk shown in FIG. 2 on which a recorded areaoccupies a part of the recordable area of the first storage layer.

FIG. 7 is a vertical cross-sectional view illustrating how data isread/written on the second storage layer of the optical disk shown inFIG. 6.

FIG. 8 is a block diagram showing a configuration by which data isread/written on the second storage layer after the first storage layerof the optical disk in FIG. 1 is fully recorded by means of the signalprocessing and controlling unit shown in FIG. 5.

FIG. 9 depicts the structure of the first and second storage layers ofan optical disk of an embodiment of the present invention and how datais read/written on the second storage layer.

FIG. 10 is a vertical cross-sectional view showing an optical disk whichhas the first and second storage layers shown in FIG. 9.

FIG. 11 depicts the structure of the first and second storage layers ofan optical disk which is a comparative example of the optical disk shownin FIG. 9 and how data is read/written on the second storage layer.

FIG. 12 depicts the structure of the first and second storage layers ofan optical disk of another embodiment of the present invention and howdata is read/written on the second storage layer.

FIG. 13 is a vertical cross-sectional view showing an optical diskequipped with the first and second storage layers shown in FIG. 12.

FIG. 14 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by which anextended area of the optical disk shown in FIG. 9 is fully recorded.

FIG. 15 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by which data isencrypted before written on the optical disk.

FIG. 16 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by whichapparatus ID information is recorded in an extended area of the opticaldisk shown in FIG. 9.

FIG. 17 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by whichencryption code information is recorded in an extended area of theoptical disk shown in FIG. 9.

FIG. 18 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by which actionsare taken according to whether or not the apparatus ID informationstored in an extended area of the optical disk shown in FIG. 9 matchesthe apparatus ID information of the optical-disk-read/write apparatus.

FIG. 19 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by whichencrypted information stored on the optical disk is decrypted.

FIG. 20 is a block diagram showing the configuration of part of thesignal processing and controlling unit shown in FIG. 5 by which data istest written in an extended area of the optical disk shown in FIG. 9.

FIG. 21 is an enlarged view showing part of a recordable area and anaddress area of an optical disk as an optical storage medium of afurther embodiment of the present invention.

FIG. 22 depicts how data is read/written in the recordable area and theaddress area of the second storage layer shown in FIG. 21.

FIG. 23 is a plan view of the optical disk shown in FIG. 21.

FIG. 24 is a block diagram showing the configuration of part of a signalprocessing and controlling unit in an optical-disk-read/write apparatusof the present embodiment by which a continuous storage area is formedin an address area of the optical disk shown in FIG. 21 based on arotation synchronized signal.

FIG. 25 is a block diagram showing the configuration of part of thesignal processing and controlling unit by which a continuous storagearea is formed in an address area of the optical disk shown in FIG. 21based on address information.

FIG. 26 is an enlarged view showing part of a recordable area, addressarea, and judgement mark area of an optical disk as an optical storagemedium of still a further embodiment of the present invention.

FIG. 27 is a block diagram showing the configuration of part of thesignal processing and controlling unit by which a continuous storagearea is formed based on a signal reproduced from the judgement mark areaof the optical disk shown in FIG. 26.

FIG. 28 is an enlarged view showing part of a recordable area and anaddress area of an optical disk as an optical storage medium of anotherembodiment of the present invention.

FIG. 29 is a block diagram showing the configuration of part of thesignal processing and controlling unit by which a continuous storagearea is formed on the optical disk shown in FIG. 28 based on a trackingservo signal.

FIG. 30 is an enlarged view showing part of a recordable area and anaddress area of an optical disk as an optical storage medium of anotherembodiment of the present invention.

FIG. 31 is a block diagram showing the configuration of part of thesignal processing and controlling unit by which a continuous storagearea is formed on the optical disk shown in FIG. 30 based on an addressinformation reproduction signal.

FIG. 32 is an enlarged vertical cross-sectional view showing thestructure of a part of the first storage layer and the second storagelayer which has a prepit area in an optical disk of another embodimentof the present invention.

FIG. 33 is a plan view showing common features in the structure ofoptical disks of another embodiment of the present invention.

FIG. 34 is a vertical cross-sectional view showing the structure ofthose types of optical disks which light enters on their surface-coatinglayer sides, among the foregoing optical disks.

FIG. 35 is an enlarged vertical cross-sectional view showing thestructure of a major part in FIG. 34.

FIG. 36 is a perspective view showing the structure of aguiding-groove-and-pits-formed layer and a part of aguiding-groove-and-pits-formed intermediate layer where a guiding grooveis formed on the optical disk.

FIG. 37 is a perspective view showing the structure of aguiding-groove-and-pits-formed layer and a part of aguiding-groove-and-pits-formed intermediate layer where pits are formedon the optical disk.

FIG. 38 is a vertical cross-sectional view showing the structure ofthose types of optical disks which light enters on their disk substratesides, among the foregoing optical disks.

FIG. 39 is a plan view showing the first storage layer of the opticaldisk shown in FIG. 34 is partly recorded.

FIG. 40 is a vertical cross-sectional view showing light beams beingtransmitted through a recorded part and a non-recorded part of theoptical disk shown in FIG. 39 before focused on the second storagelayer.

FIG. 41 is a vertical cross-sectional view showing light beamstransmitted through the first storage layer which is fully recordedbefore being focused on the second storage layer, in the optical diskshown in FIG. 39.

FIG. 42 is an enlarged vertical cross-sectional view showing a part ofthe optical disk shown in FIG. 39, where data is recorded on a part of arecordable area of the first storage layer, and light beams are focusedon prepits on the second storage layer.

FIG. 43 is an enlarged plan view of FIG. 42.

FIG. 44 is a graph showing, under the conditions illustrated in FIG. 42,the relationship between the angular position of an optical disk and theintensity (envelope) of a reproduction signal of prepit information whena light beam is projected partly covering both a recorded part and anon-recorded part in a recordable area of the first storage layer.

FIG. 45 is a waveform chart showing, under the conditions illustrated inFIG. 42, the relationship between the angular position (0 degrees and180 degrees) of optical disk and the intensity of a reproduction signalof prepit information when a light beam is projected partly coveringboth a recorded part and a non-recorded part in a recordable area of thefirst storage layer.

FIG. 46 is a waveform chart showing, under the conditions illustrated inFIG. 44, the relationship between the angular position of an opticaldisk and the intensity of a reproduction signal of prepit information,where the envelope has a mean, slice level.

FIG. 47 is a block diagram showing the configuration of a reproductioncircuit which produces a digital signal from a reproduction signal usingthe slice level shown in FIG. 46.

FIG. 48 is a graph showing, under the conditions illustrated in FIG. 42,the relationship between the angular position of an optical disk and theintensity (envelope) of a reproduction signal of prepit information whena light beam is projected partly covering both a recorded part and anon-recorded part in a recordable area of the first storage layer, wherethe reproduction signal is rid of low frequency variations.

FIG. 49 is a block diagram showing the configuration of a reproductioncircuit which produces a digital signal based on the envelope shown inFIG. 48.

FIG. 50 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk shown in FIG. 42, where thefirst storage layer has a pseudo-recording area.

FIG. 51 is an enlarge plan view showing the structure of thepseudo-recording area.

FIG. 52 is a block diagram showing the configuration by which thepseudo-recording area is formed.

FIG. 53 is an enlarge vertical cross-sectional view showing thestructure of a part of the optical disk of an embodiment of the presentinvention, where the first and second storage layers having a prepitarea.

FIG. 54 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk of FIG. 53, where the secondstorage layer has an extended blank area.

FIG. 55 is a plan view showing the structure of a part of the opticaldisk shown in FIG. 33, where the prepit area is replaced by a prepitarea in which is there provided a continuous storage area.

FIG. 56 is an enlarged vertical cross-sectional view showing thestructure of a part of the first and second storage layer in the opticaldisk shown in FIG. 55.

FIG. 57 is an enlarged plan view around the border between a recordablearea and a prepit area of the first storage layer in the optical diskshown in FIG. 55.

FIG. 58 is an enlarged vertical cross-sectional view around the bordershown in FIG. 57, where light beams pass through a recordable area and aprepit area of the first storage layer before being focused on thesecond storage layer.

FIG. 59 is a block diagram showing a configuration by which thecontinuous storage area is formed.

FIG. 60 is an enlarged vertical cross-sectional view showing thestructure of a part of the first and second storage layers, as well asthe third storage layer having a prepit area, of an optical disk ofanother embodiment of the present invention.

FIG. 61 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk shown in FIG. 60, where thefirst and second storage layers have a pseudo-recording area.

FIG. 62 is an enlarged vertical cross-sectional view showing thestructure of a part of the first storage layer which has a prepit areaand the second and the third storage layers which do not, in an opticaldisk of another embodiment of the present invention.

FIG. 63 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk shown in FIG. 62, where theprepit area is replaced by a prepit area in which is there provided acontinuous storage area.

FIG. 64 is a plan view showing a conventional optical disk.

FIG. 65 is a vertical cross-sectional view showing the structure of theoptical disk shown in FIG. 64.

FIG. 66 is an enlarged view showing a part of a recordable area and anaddress area of the optical disk shown in FIG. 64.

FIG. 67 depicts the readout and write in a recordable area and anaddress area of the second storage layer shown in FIG. 66.

FIG. 68 is a plan view showing the structure of another conventionaloptical disk.

FIG. 69 is an enlarge vertical cross-sectional view showing light beamsbeing focused on the first and second storage layer in the optical diskshown in FIG. 68.

FIG. 70 is an enlarge plan view around, the border between a recordablearea and a prepit area of the first storage layer in the optical diskshown in FIG. 68.

FIG. 71 is an enlarge plan view showing light beams being focused on thesecond storage layer after transmitted through the first storage layerin the optical disk shown in FIG. 69.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

The following will describe an embodiment of the present invention inreference to FIGS. 1-8.

Referring to FIG. 2, an optical disk (optical storage medium) 1 of thepresent embodiment has a center hole 2 at its center and a recordablearea 3 relatively close to the circumference in relation to the centerhole 2. On the recordable area 3, a spiral read/write guiding groove isformed enabling data readout and write. Broken lines in the figureindicates an innermost part 4 and an outermost part 5 of the recordablearea 3.

Referring to FIG. 3 showing a vertical cross-sectional view of theoptical disk 1, the disk 1 has on a disk substrate 6 aguiding-groove-formed layer 7, a second storage layer (second datastorage layer) 8, a guiding-groove-formed intermediate layer 9, a firststorage layer (first data storage layer) 10, and a surface-coating layer11, all the layers being stacked in this order. To read/write data inthe first storage layer 10 or the second storage layer 8 of the opticaldisk 1, a light beam 12 is always projected on the same side of the disk1, i.e., the side where the surface-coating layer 11 is provided, sothat the light beam is concentrated on the targeted, first or secondstorage layer 10, 8.

The structure of the optical disk 1 is shown in FIG. 4 in more detail.In the figure, the disk substrate 6 is made of, for example, atransparent polycarbonate substrate which is 1.2 mm thick. Theguiding-groove-formed layer 7 is made of, for example, anultraviolet-ray-setting resin layer which is 20 microns thick. On thesurface of the layer 7 which interfaces the second storage layer 8, aspiral guiding groove 13 is formed from depressions and projections. Theguiding-groove-formed layer 7 is formed, for example, by a patterntransfer technology termed 2P method.

The second storage layer 8 is made up of, for example, an AlTi-alloyreflective film 14, a ZnS—SiO₂ interference film 15, a SiN protectivefilm 16, a GeSbTe phase change recording layer 17, a SiN protective film18, and a ZnS—SiO₂ interference film 19. These layers are sequentiallystacked on the guiding-groove-formed layer 7 by sputtering.

As with the guiding-groove-formed layer 7, the guiding-groove-formedintermediate layer 9 is made of, for example, an ultraviolet-ray-settingresin layer which is 20 microns thick. On the surface of theintermediate layer 9 which interfaces the first storage layer 10, theguiding groove 13 is formed. The guiding-groove-formed layer 9 is againsimilarly formed, for example, by a pattern transfer technology termed2P method.

As with the second storage layer 8, the first storage layer 10 is madeup of, for example, a ZnS—SiO₂ interference film 20, a SiN protectivefilm 21, a GeSbTe phase change recording layer 22, a SiN protective film23, and a ZnS—SiO₂ interference film 24. These layers are sequentiallystacked on the guiding-groove-formed intermediate layer 9 by sputtering.

The surface-coating layer 11 is made of, for example, anultraviolet-ray-setting resin layer which is 80 microns thick. To formthe layer 11, an ultraviolet-ray-setting resin is applied on the firststorage layer 10 by spin coating and then cured by ultraviolet rayillumination.

The optical disk substrate 6 is, as mentioned in the foregoing, atransparent polycarbonate substrate. However, if the light beam 12 isincident only to the side of the surface-coating layer 11 as is the casewith the optical disk 1 of the present embodiment, the disk substrate 6is not necessarily transparent and may be an opaque metallic substrate.

The optical disk 1 of the present embodiment has theguiding-groove-formed layer 7 with the guiding groove 13, and theguiding-groove-formed layer 7 is formed by 2P method. Alternatively, forexample, the optical disk 1 may be formed by preparing the disksubstrate 6 by injection molding and directly forming the guiding groove13 on the optical disk substrate 6, in which case theguiding-groove-formed layer 7 is unnecessary.

The surface-coating layer 11 is formed on the first storage layer 10 byspin coating. Alternatively, the layer 11 may be a transparent sheet ofuniform thickness pasted onto the first storage layer 10.

The optical disk 1 has the guiding-groove-formed layer 7, the secondstorage layer 8, the guiding-groove-formed intermediate layer 9, thefirst storage layer 10, and the surface-coating layer 11 sequentiallystacked on the optical disk substrate 6. Alternatively, the layers maybe stacked on the optical disk substrate 6 in the order to theguiding-groove-formed layer 7, the first storage layer 10, theguiding-groove-formed intermediate layer 9, the second storage layer 8,and the surface-coating layer 11, with the light beam 12 being projectedonto the side on which the optical disk substrate 6 is located, in whichcase the films which will eventually constitute the first storage layer10 and the second storage layer 8 must be formed in the reverse orderfrom the case illustrated in FIG. 4.

An optical-disk-read/write apparatus (optical read/write apparatus) toread/write data on the optical disk 1 has the structure shown in FIG. 5.In the optical-disk-read/write apparatus 31, the optical disk 1 is fixedto the spindle 33 of the motor at the center hub and rotated.

The optical-disk-read/write apparatus 31 includes an optical system unit34 and a signal processing and controlling unit (controlling means) 35.The optical system unit 34 includes an illumination source 41, such as asemiconductor laser, a collimator lens 42, a beam splitter 43, anobjective lens 44, a double-axis actuator 45, a collective lens 46 and alight-receiving element 47. The objective lens 44 is supported by thedouble-axis actuator 45 and moved along a focusing direction and atracking direction. The light-receiving element 47 includes areproduction signal detecting element, a focus error signal detectingelement, and a tracking error signal detecting element. The outputs ofthe detecting elements are fed to the signal processing and controllingunit 35.

The optical system unit 34 is driven by a slide driving unit (not shown)so as to reciprocally move along the radius of the optical disk 1.

The signal processing and controlling unit 35 implements various signalprocessing and controlling operations. For example, the illuminationsource 41 is controlled in terms of output power in read/writeoperations. The double-axis actuator 45 is controlled in response to theoutputs of the focus error signal detecting element and the trackingerror signal detecting element, to control the focusing and trackingactions of the objective lens 44. The signal processing and controllingunit 35 further controls the slide driving unit and hence the movementof the optical system unit 34 along the radius of the optical disk 1.Thereby, the optical system unit 34, hence the objective lens 44, ismoves to a position where the unit 34 can read/write data on apredetermined track. Other control actions of the signal processing andcontrolling unit 35 will be described later.

In the optical-disk-read/write apparatus 31, the light beam 12 isconcentrated on either the first storage layer 10 or the second storagelayer 8 by the mechanism discussed in the foregoing, so that data isread/written from/into either the first storage layer 10 or the secondstorage layer 8 along the guiding groove 13.

In the present embodiment, in the optical-disk-read/write apparatus 31,data is read/written from/into the second storage layer 8 only after therecordable area 3 of the first storage layer 10 is fully recorded.Actions in this case are implemented by the signal processing andcontrolling unit 35 which controls the optical system unit (illuminatingmeans) 34 and the slide driving unit (illuminating means).

Actions in this case are shown in FIG. 1. Referring to that figure, whenthe read/write light beam 12 is projected to the second storage layer 8,the recordable areas 3 of the first storage layer 10 are fully recordedin advance (shown in black). Therefore, the light beam 12 is transmittedthrough the fully recorded, first storage layer 10 and projected to thesecond storage layer 8.

Assuming the foregoing structure, the following will describe how theoptical-disk-read/write apparatus 31 reads/writes data on the opticaldisk 1.

In the optical-disk-read/write apparatus 31, the light beam 12 emittedby the illumination source 41 is collimated by the collimator lens 42,transmitted through the beam splitter 43, before entering the objectivelens 44. Then, the light beam 12 is focused by the objective lens 44 oneither the first storage layer 10 or the second storage layer 8 of theoptical disk 1. The reflection from the optical disk 1 passes throughthe objective lens 44, deflected by the beam splitter 43, and focused bythe collective lens 46 on the light-receiving element 47.

Thereafter, based on the output of the light-receiving element 47, thesignal processing and controlling unit 35 controls the double-axisactuator 45 and hence the objective lens 44 for its precise focusing andtracking actions. Thus, in the optical-disk-read/write apparatus 31, toread/write data from/into either the first storage layer 10 or thesecond storage layer 8, the light beam 12 is focused on that storagelayer along the guiding groove 13.

In the foregoing situation, the following will describe how theoptical-disk-read/write apparatus 31 reads/writes data on the opticaldisk 1, provided that data is recorded starting with the innermost part4 of the recordable area 3 of the first storage layer 10 of the opticaldisk 1 until data fills part of the recordable area 3 of the firststorage layer 10 and then the operation moves to reading/writing data inthe second storage layer 8. It is also supposed that the optical disk 1is a high-to-low medium such that the interval area is more reflectivethan the recording mark area and data is recorded by phase change.

As a result of recording in the first storage layer 10, as shown inFIGS. 6, 7, a recorded area 51 (shown by hatched lines) shown isproduced covering the innermost part 4 of the recordable area 3 of thefirst storage layer 10 up to partway of the recordable area 3.

Here, the first storage layer 10 is more optically transmissive in therecorded area 51 than other areas. As a result, the light beam 12projected on the second storage layer 8 is more intense when it isconcentrated on the second storage layer 8 if it has passed through therecorded area 51 than if it has passed through an area other than therecorded area 51 (a non-recorded area). In other words, in recordingdata into the second storage layer 8, the light beam 12 varies inintensity when it reaches the second storage layer 8 after passingthrough the first storage layer 10, depending on whether it has comethrough the recorded area 51. In this case, to record data into thesecond storage layer 8, a complex write system is required which canvary the light beam 12 in intensity depending on whether there are anyrecords stored in the first storage layer 10.

The same description applies to the case where data is read from thesecond storage layer 8, and a similarly complex read system is required,because the return light reflected off the second storage layer 8changes in quantity depending on whether the light beam 12 has passedthrough the recorded area 51 of the first storage layer 10.

Accordingly, in the optical-disk-read/write apparatus 31 of the presentembodiment, as shown in FIG. 1, data is read/written from/into thesecond storage layer 8 only after the recordable area 3 of the firststorage layer 10 is fully recorded. In other words, to record data onthe optical disk 1, the optical-disk-read/write apparatus 31 firstwrites data in the first storage layer 10, and only after the recordablearea 3 of the first storage layer 10 is recorded to its full capacity,starts writing or reading data into/from the second storage layer 8.

The operation ensures that in the read/write operation as to the secondstorage layer 8, the light beam 12 projected on the second storage layer8 always passes through the fully recorded, first storage layer 10before entering the second storage layer 8. In both read and writeoperations, the light beam 12 has a constant intensity when it reachesthe second storage layer 8, which eliminates the need to use a complexread/write system to control the intensity of the light beam 12. Stableread/write operations are thus achieved.

To carry out such operations, the signal processing and controlling unit35 is provided with a write-start address producing circuit 81 and anilluminating-unit-controlling circuit 82 as shown in FIG. 8. Theilluminating unit controlled by the illuminating-unit-controllingcircuit 82 is inclusive of, for example, the optical system unit 34 andthe slide driving unit.

To write data on the optical disk 1, first, a recording status managingsignal is reproduced from data recorded in a recording status managingarea of the optical disk 1, and the signal is all recorded in thewrite-start address producing circuit 81 in the signal processing andcontrolling unit 35. The recording status managing area is provided at aparticular position in the first storage layer 10. The recording statusmanaging area may contain the title of the recorded material, as well asan address representing a recording range.

Thereafter, the write-start address producing circuit 81 produces awrite-start address for the optical disk 1, and theilluminating-unit-controlling circuit 82 controls focus and tracking soas to move the light beam spot to the write-start address. This actiontriggers recording in the recordable area 3 of the first storage layer10.

Thereafter, data is written to the first storage layer 10 to its fullcapacity, that is, until the last address of the first storage layer 10is detected. If data is written to the second storage layer 8 without abreak, the light beam 12 is concentrated on the second storage layer 8to similarly carry out recording in the recordable area 3 of the secondstorage layer 8.

Embodiment 2

The following will describe another embodiment of the present inventionin reference to FIGS. 9-11. An optical disk 61 of the present embodimentis operational with the optical-disk-read/write apparatus 31 which worksas described in the foregoing.

The optical disk 61 of the present embodiment has extended areas 62 inthe innermost part 4 a and the outermost part 5 a of the recordable area3 a of the first storage layer 10 as shown in FIGS. 9, 10. Therefore,the innermost part 4 a of the first storage layer 10 extends furtherinwards in relation to the diameter of the optical disk 1 when comparedto the innermost part 4 b of the second storage layer 8. The outermostpart 5 a of the first storage layer 10 extends further outwards inrelation to the diameter when compared to the outermost part 5 b of thesecond storage layer 8.

In other words, the recordable area 3 a of the first storage layer 10 isgreater than the recordable area 3 b of the second storage layer 8 bythe extended areas 62 in the innermost part 4 a and in the outermostpart 5 a. FIG. 9 is used to show the innermost parts 4 a, 4 b and theoutermost parts 5 a; 5 b for convenience.

No matter how large or small the extended areas 62 are, their mereprovision reduces the loss in intensity of a light beam projected to therecordable area 3 b of the second storage layer 8 as will be describedlater. To further and preferably reduce the loss in intensity of such alight beam, each extended area 62 should be specified enough wide (orlong when measured along a diameter of the optical disk 1) that thelight beam 12 may not spill out of the recordable area 3 a, inclusive ofthe extended area 62, of the first storage layer 10 regardless whetherthe light beam 12 is focused on the innermost part 4 b or the outermostpart 5 b of the recordable area 3 b of the second storage layer 8.

FIG. 11 shows an optical disk for comparison to explain the functions ofthe optical disk 61. In the optical disk 63, the recordable area of thefirst storage layer 10 is as large as that of the second storage layer8. The innermost part 4 and the outermost part 5 in the first storagelayer 10 are positioned directly above and occupy the same area as theirequivalents of the second storage layer 8.

As shown in FIGS. 9, 11, in both optical disks 61, 63, the first storagelayer 10 and the second storage layer 8 each have a guiding groove 13,and the first storage layer 10 is fully recorded along the guidinggroove 13 up to either the innermost part 4 a, 4 or the outermost part 5a, 5 of the recordable area 3 a, 3. In the figures, the fully recordedstatus of the guiding groove 13 is shown by bold lines. In other words,in the readout/write on the optical disks 61, 63, theoptical-disk-read/write apparatus 31, again, first writes data in therecordable area 3 a, 3 of the first storage layer 10 to its fullcapacity before data is read/written in the recordable area 3 b, 3 ofthe second storage layer 8.

In the arrangement, as to the optical disk 63 equipped with recordableareas 3 with no extended area 62 on the first storage layer 10, thelight beam 12 b projected on the recordable area 3 of the second storagelayer 8 somewhere midway in relation to the radius of the disk toread/write data in the second storage layer 8 passes entirely throughthe recordable area (fully recorded area) 3 where the first storagelayer 10 exhibits a relatively high transmittance.

By contrast, the light beam 12 c, if projected close to the innermostpart 4 or the outermost part 5 of the second storage layer 8, does notentirely passes through the recordable area (fully recorded area) 3where the first storage layer 10 exhibits a relatively hightransmittance, but partially passes through unrecordable areas 64 otherthan the recordable area 3 where the first storage layer 10 exhibits arelatively lower transmittance. Accordingly, the light beam 12 c is lessintense than the light beam 12 b. Therefore, in reading/writing data inthe second storage layer 8, the light beam decreases, i.e., varies, inintensity in the innermost part 4, the outermost part 5, and theirneighborhoods of the recordable area 3 of the second storage layer 8,making it difficult to perform stable read/write operations across theentire recordable area 3 of the second storage layer 8.

By contrast, the optical disk 61 of the present embodiment is providedwith recordable areas 3 a with extended areas 62 on the first storagelayer 10. Thus, the light beam projected on the recordable area 3 b ofthe second storage layer 8 to read/write data in the second storagelayer 8 illuminates passes through the recordable area (fully recordedarea) 3 a where the first storage layer 10 exhibits a relatively hightransmittance not only when the light is directed on the second storagelayer 8 somewhere midway in relation to the radius of the disk, but alsowhen the light is directed on the innermost part 4 b or the outermostpart 5 b of the second storage layer 8.

Thus, with the optical disk 61 of the present embodiment, the light beamprojected on the recordable area 3 b of the second storage layer 8always becomes the light beam 12 b which has passed through therecordable area (fully recorded) 3 a where the first storage layer 10exhibits a relatively high transmittance. The light beam does not varyin intensity whether data is read/written from/into any part of therecordable area 3 b of the second storage layer 8. Stable read/writeoperations are thus achieved.

To perform read/write operation on the second storage layer 8, the lightbeam 12 projected on the first storage layer 10 has a radius notexceeding the thickness of the guiding-groove-formed intermediate layer9. Therefore, the extended area 62 is sufficiently wide (or long whenmeasured along a diameter of the optical disk) if it is as wide (orlong) as the guiding-groove-formed intermediate layer 9 is thick. If theguiding groove 13 on the first storage layer 10 is not concentric to theguiding groove 13 on the second storage layer 8, the extended area 62should be designed as wide as the guiding-groove-formed intermediatelayer 9 is thick, plus the deviation.

FIG. 9 is a schematic view, and the extended area 62 is shown as wide asthe area covering two guiding grooves 13. However, in practice, theextended area 62 is as wide as the area covering at least 60 guidinggrooves 13, because the guiding grooves 13 have a pitch of about 0.3microns and the guiding-groove-formed intermediate layer 9 has athickness of about 20 microns.

In addition, the extended area 62 may be formed in only one of theinnermost part 4 a and the outermost part 5 a of the first storage layer10, in which case the extended area 62 is functional as described in theforegoing where it is formed.

Embodiment 3

The following will describe a further embodiment of the presentinvention in reference to FIGS. 12-20. An optical disk 71 of the presentembodiment is operational with the optical-disk-read/write apparatus 31which works as described in the foregoing.

The optical disk 61 has an extended area 62 in the innermost part 4 aand the outermost part 5 a of the recordable area 3 a of the firststorage layer 10. The optical disk 71 of the present embodiment has afully prerecorded pseudo-recording area 72 in an area which is anequivalent of the extended area 62 as shown in FIGS. 12, 13. Therefore,on the optical disk 71 of the present embodiment, the recordable area 3where ordinary information is recorded is as great on the first storagelayer 10 as it is on the second storage layer 8. The pseudo-recordingarea 72 may be provided before the optical disk 71 is shipped out, forexample.

In the arrangement, to perform normal read/write on the optical disk 71,similarly to the foregoing case, the optical-disk-read/write apparatus31 first writes data in the first storage layer 10, and only after therecordable area 3 is recorded to its full capacity, starts writing orreading in recordable area 3 of the second storage layer 8, in whichcase, the pseudo-recording area 72 is already fully recorded.

As mentioned in the foregoing, the optical disk 71 of the presentembodiment has a pseudo-recording area 72 inside the innermost part 4 band outside the outermost part 5 b of the recordable area 3 of the firststorage layer 10 in relation to the diameter of the disk 71. Therefore,to perform read/write in the second storage layer 8, similarly to thecase of the optical disk 61, the light beam projected on the recordablearea 3 of the second storage layer 8 always becomes the light beam 12 bhaving passed through a fully recorded area where the first storagelayer 10 has a relatively high transmittance. The light beam does notvary in intensity whether data is read/written from/into any part of therecordable area 3 of the second storage layer 8. Stable read/writeoperations are thus achieved.

Further, unlike the optical disk 61, the optical disk 71 has therecordable area 3 which is as large on the first storage layer 10 as onthe second storage layer 8, and the guiding grooves 13 on the recordablearea 3 may share a common format. As a result, the optical system unit34 is controlled in terms of its position in performing read/write onthe first storage layer 10 in the same manner as in performingread/write on the second storage layer 8.

The pseudo-recording area 72 may be formed on the optical disk 61 withan extended area 62, by the optical-disk-read/write apparatus 31recording data in that extended area 62 to the full capacity. Theoptical disk 71 can be thus made from an optical disk 61. In such anarrangement, it is not necessary to fabricate an optical disk 71 byforming a pseudo-recording area 72 on an optical disk 61 prior toshipment. The omission of the step allows for reduction of the cost ofthe optical disk 61 (71).

The optical-disk-read/write apparatus 31 forms a pseudo-recording area72 by fully recording the extended area 62 prior to ordinary recordingin the first storage layer 10, for example, when the optical disk 61 isloaded into the optical-disk-read/write apparatus 31. In this case, theoptical-disk-read/write apparatus 31 first reads data from an extendedarea 62 of the loaded optical disk 61, and if the extended area 62 isnot fully recorded, records data in the area 62 to its full capacity.The process is controlled by the signal processing and controlling unit35 of the optical-disk-read/write apparatus 31.

To implement such control, the signal processing and controlling unit 35is provided with an extended-area-recording-status-checking circuit 83and an illuminating-unit-controlling circuit 82 (detailed in theforegoing) as shown in FIG. 14.

In the arrangement, as the optical disk 61 is loaded, theoptical-disk-read/write apparatus 31 first reads data from its extendedarea. The extended-area-recording-status-checking circuit 83 checksbased on a reproduction signal from the extended area 62 whether or notthe extended area 62 is fully recorded. If the check turns out that theextended area 62 is not fully recorded, theextended-area-recording-status-checking circuit 83 regards the loadedoptical disk 61 as being never used, and supplies anextended-area-writing-instruction signal to theilluminating-unit-controlling circuit 82 prior to the start of arecording action carried out on the first storage layer 10. Uponreceiving that signal, the illuminating-unit-controlling circuit 82controls the illuminating unit so as to make the extended area 62 on theoptical disk 61 fully recorded.

Meanwhile, if the check turns out that the extended area 62 is fullyrecorded, the extended-area-recording-status-checking circuit 83 regardsthe loaded optical disk 61 as being already used, and supplies a normalwriting-instruction signal to the illuminating-unit-controlling circuit82. Upon receiving that signal, the illuminating-unit-controllingcircuit 82 controls the illuminating unit so as to perform an ordinaryrecording action on the optical disk 61.

The pseudo-recording area 72 may store absolutely nonsense ormeaningless information. Alternatively, if the optical disk 61 isprovided with the pseudo-recording area 72 before being shipped out, thepseudo-recording area 72 may contain a disk ID (identificationinformation) or encryption code information (encryption information)which match that particular optical disk 61, but not the other disks.

If the pseudo-recording area 72 contains encryption code information,the optical-disk-read/write apparatus 31 may record information in therecordable area 3 of the optical disk 71 only after the apparatus 31encrypts the information based on the encryption code information. Inthis case, to record information on the optical disk 71, theoptical-disk-read/write apparatus 31 first reads the encryption codeinformation of pseudo-recording area 72 and encrypts information to berecorded, based on the encryption code information. In addition, toreproduce information from an encrypted optical disk 71, theoptical-disk-read/write apparatus 31 decrypts information after readoutfrom the recordable area 3. These processes are controlled by the signalprocessing and controlling unit 35.

In this case, the optical-disk-read/write apparatus 31 cannot decryptinformation which is read out from the optical disk 71 unless theapparatus 31 is equipped with a function to decrypt the encryptedinformation, which makes it possible to prevent the illegal copying andother uses of the optical disk 71.

As mentioned in the foregoing, to record information on the optical disk71 after encrypting it based on the encryption code information in thepseudo-recording area 72, the signal processing and controlling unit 35is provided with the encrypting circuit 84 and theilluminating-unit-controlling circuit 82 as shown in FIG. 15.

In the arrangement, prior to taking a recording action on the opticaldisk 71, the encryption code information is reproduced which is recordedin advance in the pseudo-recording area 72 of the optical disk 71. Theencrypting circuit 84 encrypts recording information based on theencryption code information and supplies the encrypted recordinginformation to the illuminating-unit-controlling circuit 82. Theilluminating-unit-controlling circuit 82 controls the illuminating unitso that the recording information is recorded on the optical disk 71.

In addition, if the pseudo-recording area 72 contains diskidentification information, it is possible to prevent the illegalcopying and other uses of the optical disk 71 by managing the diskidentification information in the optical-disk-read/write apparatus 31or in a server or the like connected to the optical-disk-read/writeapparatus 31. The managing of the disk identification information refersto the processing to count the times the optical disk 71 is used tolimit the times the disk is used, for example.

In addition, provided that the pseudo-recording area already containsdisk identification information or encryption code information,designing the pseudo-recording area 72 as a read-only area prohibitsrewriting these sets of information. This further appropriately preventsthe illegal copying and other uses of the optical disk 71.

In addition, as mentioned earlier, when the optical-disk-read/writeapparatus 31 forms the pseudo-recording area 72 on the optical disk 61to form the optical disk 71 from the optical disk 61, theoptical-disk-read/write apparatus 31 may record, in the pseudo-recordingarea 72, the apparatus ID information which is unique to theoptical-disk-read/write apparatus 31 or encryption code informationwhich is unique to the optical-disk-read/write apparatus 31.

When the optical-disk-read/write apparatus 31 records the apparatus IDinformation on the pseudo-recording area 72, the signal processing andcontrolling unit 35 in the optical-disk-read/write apparatus 31 isequipped with an identification-information-presence-checking circuit 85and the illuminating-unit-controlling circuit 82 as shown in FIG. 16.

In the arrangement, as the optical disk 61 is loaded, theoptical-disk-read/write apparatus 31 first reads the extended area. Theidentification-information-presence-checking circuit 85 checks based ona reproduction signal from the extended area 62 whether the apparatus IDinformation is present in the extended area 62. If the check turns outthat the extended area 62 contains no apparatus ID information, theidentification-information-presence-checking circuit 85 regards theloaded optical disk 61 as being as being never used, and supplies anidentification-information-writing-instructing signal to theilluminating-unit-controlling circuit 82 prior to the start of arecording action on the first storage layer 10. Upon receiving thatsignal, the illuminating-unit-controlling circuit 82 controls theilluminating unit so as to record the apparatus ID information in theextended area 62 of the optical disk 61. The apparatus ID information iscontained in the signal processing and controlling unit (identificationinformation storing means) 35.

Meanwhile, if the check turns out that the extended area 62 holdsapparatus ID information, theidentification-information-presence-checking circuit 85 regards theloaded optical disk 61 as being already used, and supplies a normalread/write-instructing signal to the illuminating-unit-controllingcircuit 82. Upon receiving that signal, theilluminating-unit-controlling circuit 82 controls the illuminating unitso as to perform an ordinary read/write action on the optical disk 61.

In addition, to record encryption code information in thepseudo-recording area 72 using the optical-disk-read/write apparatus 31,the signal processing and controlling unit 35 in theoptical-disk-read/write apparatus 31 is equipped with anencryption-information-presence-checking circuit 86 and theilluminating-unit-controlling circuit 82 as shown in FIG. 17.

In the arrangement, as the optical disk 61 is loaded, theoptical-disk-read/write apparatus 31 first reads the extended area 62.The encryption-information-presence-checking circuit 86 checks based ona reproduction signal from the extended area 62 whether the encryptioncode information (encryption information) is present in the extendedarea 62. If the check turns out that the extended area 62 contains noencryption code information, theencryption-information-presence-checking circuit 86 regards the loadedoptical disk 61 as being never used, and supplies anencryption-information-reading signal to theilluminating-unit-controlling circuit 82 prior to the start of arecording action on the first storage layer 10. Upon receiving thesignal, the illuminating-unit-controlling circuit 82 controls theilluminating unit to record encryption code information in the extendedarea 62 of the optical disk 61. The encryption code information iscontained in the signal processing and controlling unit (encryptioninformation storing means) 35.

Meanwhile, if the check turns out that the extended area 62 holdsencryption code information, theencryption-information-presence-checking circuit 86 regards the loadedoptical disk 61 as being already used, and supplies an ordinaryread/write-instructing signal to the illuminating-unit-controllingcircuit 82. Upon receiving the signal, the illuminating-unit-controllingcircuit 82 controls the illuminating unit so as to perform an ordinaryread/write action on the optical disk 61.

In addition, as mentioned earlier, when the optical-disk-read/writeapparatus 31 records apparatus ID information or encryption codeinformation in the pseudo-recording area 72 (extended area 62), anarrangement may be made so that only the optical-disk-read/writeapparatus 31 which did that recording can reproduce information from therecordable area 3 of the optical disk 71 (61).

Processing in this case is done as below, for example. Supposing thatthe pseudo-recording area 72 of the optical disk 71 holds apparatus IDinformation, to read the optical disk 71, the optical-disk-read/writeapparatus 31 first reproduce the apparatus ID information from thepseudo-recording area 72 of the optical disk 71, and then reads datafrom the optical disk 71 only when the apparatus ID information readoutmatches the apparatus ID information of the optical-disk-read/writeapparatus 31 as a result of checking.

To realize these actions, the signal processing and controlling unit 35is equipped with an identification-information-match-checking circuit 87and the illuminating-unit-controlling circuit 82 as shown in FIG. 18.

In the arrangement, as the optical disk 71 is loaded, theoptical-disk-read/write apparatus 31 first reads the pseudo-recordingarea 72. The identification-information-match-checking circuit 87compares the apparatus ID information obtained from the reproductionsignal read out from the pseudo-recording area 72 with the apparatus IDinformation assigned to the optical-disk-read/write apparatus 31 tocheck whether the two sets of apparatus ID information match. If thecheck turns out that the two sets of apparatus ID information match eachother, a read/write-instructing signal is supplied to theilluminating-unit-controlling circuit 82. Upon receiving the signal, theilluminating-unit-controlling circuit 82 controls the illuminating unitso as to perform a read/write action on the optical disk 71.

Meanwhile, if the two sets of apparatus ID information does not matcheach other, the identification-information-match-checking circuit 87supplies an identification-information-match-display signal representingthe situation to the illuminating-unit-controlling circuit 82. Uponreceiving that signal, the illuminating-unit-controlling circuit 82causes a display unit (not shown) to display a notice to that situation,for example. In this case, no data is read nor written on the opticaldisk 71.

In addition, if the recordable area 3 of the optical disk 71 holdsinformation which is encrypted based on encryption code information, toread the optical disk 71, the optical-disk-read/write apparatus 31decrypts the information read out from the recordable area 3 based onthe encryption code information of the optical-disk-read/write apparatus31. The decryption is done, as shown in FIG. 19, in a decrypting circuit88 in the signal processing and controlling unit 35. In thesecircumstances, the information read out from the recordable area 3 canbe decrypted only when the encryption code information used with theoptical disk 71 matches the encryption code information provided to theoptical-disk-read/write apparatus 31. The arrangement enables preventionof copying, legal or illegal, of the optical disk 71.

In addition, the extended area 62 of the optical disk 61 can be used asa test write area as follows.

For example, the most suitable light beam intensity to write data on theoptical disk 61, that is the most suitable writing power, variesdepending on changes in various factors including ambient temperature.Therefore, the optical-disk-read/write apparatus 31 usually test writesdata on the optical disk to calculate the most suitable writing power.Accordingly, on the optical disk 61, the extended area 62 is at leastpartly used as a test write area. The arrangement eliminates the need toseparately provide a test write area on the optical disk 61 and enablesefficient use of the recordable area 3 of the optical disk 61.

To implement these actions, the signal processing and controlling unit35 is provided with a test-write-controlling circuit 89, awriting-power-checking circuit 90, and the illuminating-unit-controllingcircuit 82 as shown in FIG. 20.

In the arrangement, to write data on the optical disk 61, atest-write-recording instruction is given to the test-write-controllingcircuit 89 prior to writing in the first storage layer 10. Thus, theextended area 62 of the optical disk 61 is test written (recorded astest write). The test write is done with the writing power varied bylittle amounts.

Next, the data recorded in the test write is reproduced, and thereproduction signal is supplied to the writing-power-checking circuit90. The writing-power-checking circuit 90 determines the most suitablewriting power to record data on the optical disk 61 based on thereproduction signal. Thereafter, the information representative of themost suitable writing power is supplied to theilluminating-unit-controlling circuit 82 which controls the illuminatingunit so that data is written on the optical disk 61 using the mostsuitable writing power. The arrangement always enables recording underthe most suitable conditions regardless of changes in various factorsincluding ambient temperature and resultant changes in the recordingsensitivity of the optical disk 61.

Throughout the embodiments above, it was supposed that the optical disksare all high-to-low phase change types of storage media whose intervalareas have higher reflectance, i.e., lower transmittance, than therecording mark areas. The foregoing arrangements are however applicableto those optical disks that may be low-to-high phase change types ofstorage media whose interval areas have lower reflectance, i.e., highertransmittance, than the recording mark areas.

Embodiment 4

The following will describe another embodiment of the present inventionin reference to FIGS. 21-25.

As shown in FIG. 23, an optical disk (optical storage medium) 101 of thepresent embodiment has a center hole 102 at its center and a recordablearea 103 outside the center hole 102 in relation to a diameter. Theinnermost part and the outermost part of the recordable area 103 areshown by broken lines. The optical disk 101 employs a lumped addressscheme: an address area 104 is provided occupying a predeterminedangular part of the recordable area 103, and address information isrepresented by radially arranged address pit rows in the address area104. In a non-address area 105, which is the part of the recordable area103 other than the address area 104, there is provided a spiralingread/write guiding groove along which information can be read/written.

Like the optical disk 1, the optical disk 101 is arranged as shown inFIG. 3 and FIG. 4.

FIG. 21 shows an enlarged view of a part of the optical disk 101, wherean address area 104 and non-address areas 105 adjacent to the addressarea 104 are depicted. Each non-address area 105 stores recording marks111 formed by projection of a light beam 12 along the spiraling guidinggroove 13. The recording mark 111 differs from surrounding portions inoptical transmittance.

In the address area 104, address tracks 113 made of address pits 112 areprovided to extend from the guiding grooves 13 in the non-address areas105. The address area 104 includes recorded areas where transmittancehas changed and non-recorded areas where transmittance has not changed.Concretely, the (continuous) address area 104 where transmittance haschanged is formed by continuously recording alternate address tracks 113in relation to a diameter of the optical disk 101 by continuouslyprojecting a light beam 12. In other words, one of two address tracks113 in the address area 104 which are adjacent in the relation to adiameter of the optical disk 101 is continuously recorded, whereas theother is unrecorded.

The optical-disk-read/write apparatus (optical read/write apparatus) forreading/writing the optical disk 101 was already described in referenceto FIG. 5, as with the optical disk 1.

For the optical-disk-read/write apparatus 31 to read/write data on theoptical disk 101, the first storage layer 10 is read/written as shown inFIG. 22 by focusing and projecting the light beam 12 onto the firststorage layer 10 while tracking the guiding groove 13 on the firststorage layer 10 and controlling the light beam intensity. In addition,the second storage layer 8 is read/written by focusing and projectingthe light beam 12 onto the second storage layer 8 while tracking theguiding groove 13 on the second storage layer 8 and controls the lightbeam intensity.

In this situation, it is supposed that the optical disk 101 is, forexample, a high-to-low phase change type of storage medium in which inthe first storage layer 10 and the second storage layer 8, intervalareas between the recording marks 111 have a higher reflectance, i.e.,lower transmittance, than the recording marks 111.

In this case, in the non-address area 105 on the first storage layer 10,the recording marks 111 have a higher transmittance. Therefore,referring to FIG. 22, the light beam 12 e projected onto the secondstorage layer 8 after passing trough a portion of the first storagelayer 10 where the recording marks 111 are present has a greaterintensity than the light beam projected onto the second storage layer 8without passing through that portion where the recording marks 111 arepresent. Likewise, since the address area 104 on the first storage layer10 has continuous storage areas 114, the light beam 12 f projected ontothe second storage layer 8 after passing through the address area 104has a greater intensity than the light beam projected onto the secondstorage layer 8 after passing through the address area in the case wherethere are no continuous storage areas 114. Therefore, as to the opticaldisk 101, the intensity of the light beam 12 f projected onto the secondstorage layer 8 after passing through an address area 104 on the firststorage layer 10 can be made closer to the intensity of the light beam12 e projected onto the second storage layer 8 after passing through thenon-address area 105 on the first storage layer 10.

As a result, as to the optical disk 101 employing a lumped addressscheme, the light beam intensity on the second storage layer 8 can beretained at a substantially constant value regardless of whether thelight is the light beam 12 e passing through the non-address area 105 onthe first storage layer 10 or the light beam 12 f passing through theaddress area 104 on the first storage layer 10, enabling stable anddesirable read/write on the second storage layer 8.

Besides, on the optical disk 101 of the present embodiment, a continuousstorage area 114 appears on alternate address tracks 113 in relation toa diameter of the optical disk 101. Therefore, when the light beam 12 isfocused on the second storage layer 8 as shown in FIG. 22, in the casewhere a beam spot 115 formed by the light beam 12 forms on the firststorage layer 10 as shown in FIG. 21, the sum of the areas of therecording marks 111 included in the area of the beam spot 115 in thenon-address area 105 on the first storage layer 10 is substantiallyequal to the sum of the continuous storage areas 114 included in thearea of the beam spot 115 in the address area 104. Thus, the intensityof the light beam 12 f projected onto the second storage layer 8 afterpassing through an address area 104 on the first storage layer 10 can bemade substantially equal to the intensity of the light beam 12 eprojected onto the second storage layer 8 after passing through thenon-address area 105 on the first storage layer 10.

In FIG. 21, ten address pits 112 are shown forming an address track 113.However, FIG. 21 is only a schematic figure, and in practice, an addresstrack 113 is made up of 1000 or more address pits 112 of variouslengths.

The continuous storage area 114 on the optical disk 101 may be formedprior to the shipment of the optical disk 101 or by theoptical-disk-read/write apparatus 31 based on reproduced addressinformation when the optical disk 101 is loaded in theoptical-disk-read/write apparatus 31. In the arrangement, the opticaldisk 101 does not need any particular arrangement that enables thedetermination whether to form a continuous storage area 114 in theaddress track 113.

To implement the actions, the signal processing and controlling unit 35in the optical-disk-read/write apparatus 31 has a recorded/unrecordedswitching circuit 121 and an illuminating-unit-controlling circuit 122as shown in FIG. 24. The illuminating unit controlled by theilluminating-unit-controlling circuit 122 is inclusive of an opticalsystem unit 34 and a slide driving unit.

In the arrangement, the signal processing and controlling unit 35 feedsa rotation synchronized signal produced in synchronism with the rotationof the optical disk 101 to the recorded/unrecorded switching circuit121. The recorded/unrecorded switching circuit 121 checks based on therotation synchronized signal for every turn of the optical disk 101whether to make the address track 113 a continuous storage area 114,that is, whether to continuously recorded the address track 113. Here,as mentioned earlier, the check is done so that alternate address tracks113 are continuous storage areas 114.

If the address track 113 is caused to be a continuous storage area 114,the recorded/unrecorded switching circuit 121 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit and continuously record the address track 113.

Meanwhile, if the address track is caused to be unrecorded, therecorded/unrecorded switching circuit 121 feeds anaddress-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data. In this case, address information isreproduced.

In addition, to implement the actions, the signal processing andcontrolling unit 35 in the optical-disk-read/write apparatus 31 mayinclude an arrangement shown in FIG. 25 which differs from thearrangement in FIG. 24. In that arrangement, the signal processing andcontrolling unit 35 has a subsequent-address-track-recorded/unrecordedchecking circuit 123 and the illuminating-unit-controlling circuit 122.

In this arrangement, the subsequent-address-track-recorded/unrecordedchecking circuit 123 determines based on the address informationobtained from the address area 104 whether to make the address track 113a continuous storage area 114. In other words, as mentioned in theforegoing, in the case where alternate address tracks 113 are designatedas continuous storage areas 114, regardless whether to make thecurrently scanned address track 113 a continuous storage area 114, thataddress track 113 is read first of all, and it is determined based onthe obtained address information whether to make a subsequent addresstrack 113 a continuous storage area 114.

In the arrangement, in the signal processing and controlling unit 35,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to first read that address track 113 with which the processis started and obtain an address information reproduction signal of theaddress track 113. The address information reproduction signal is fed tothe subsequent-address-track-recorded/unrecorded checking circuit 123.

Upon receiving the address information reproduction signal, thesubsequent-address-track-recorded/unrecorded checking circuit 123 basedon that signal determines whether to make a subsequent address track acontinuous storage area 114.

If the subsequent address track 113 is to be continuously recorded, thesubsequent-address-track-recorded/unrecorded checking circuit 123transmits a subsequent-address-track-continuous-recording-instructingsignal to the illuminating-unit-controlling circuit 122. Upon receivingthe signal, the illuminating-unit-controlling circuit 122 controls theilluminating unit so as to make the subsequent address track 113 acontinuous storage area 114.

Meanwhile, if the subsequent address track 113 is to be unrecorded, thesubsequent-address-track-recorded/unrecorded checking circuit 123 feedsa subsequent address-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data.

In the arrangement in FIG. 24, if the process of forming a continuousstorage area 114 in the address area 104 is suspended before completionand resumed again thereafter, it is unknown whether the last addresstrack 113 processed before the suspension is now a continuous storagearea 114 or not. Therefore, adjacent address tracks 113 are possiblyboth continuous storage areas 114. In contrast, such situations areprevented from happing in the arrangement in FIG. 25, the addressinformation is being always checked to determine whether to make thesubsequent address track 113 continuously recorded or unrecorded at all.

Embodiment 5

The following will describe another embodiment of the present inventionin reference to FIG. 26 and FIG. 27.

An optical disk 131 of the present embodiment has a judgement mark area132 between a non-address area 105 and the head of an address area 104as shown in FIG. 26 which is an enlarged view around the head of theaddress area 104.

In the judgement mark area 132 there are formed judgement pits(judgement marks) 133, 134 by which it is determined whether the addresstrack 113 in the address area 104 is made a continuous storage area 114or not. The judgement pits 133, 134 are located between the guidinggroove 13 in a non-address area 105 and its succeeding address track 113in the address area 104.

The judgement pits 133 show that the address tracks 113 are not to bemade continuous storage areas 114 and are positioned in the judgementmark area 132 near the non-address area 105. Meanwhile, the judgementpits 134 show that the address tracks 113 are to be made continuousstorage areas 114 and are positioned in the judgement mark area 132 nearthe address area 104. The judgement pits 133 exist at positions shiftedalong the tracks when compared to the judgement pits 134. In the presentembodiment, as mentioned earlier, alternate address tracks 113 are madecontinuous storage area 114; therefore, the judgement pits 133, 134appear alternately along a diameter of the optical disk 131.

To appropriately make the address tracks 113 in the address area 104continuous storage areas 114 using the judgement pits 133, 134, thesignal processing and controlling unit 35 in the optical-disk-read/writeapparatus 31 is provided with a recorded/unrecorded-checking circuit 124and the illuminating-unit-controlling circuit 122 as shown in FIG. 27.

In the arrangement, upon detecting a judgement mark reproduction signalwhich is a signal reproduced from the judgement pits 133, 134, thesignal processing and controlling unit 35 feeds that signal to therecorded/unrecorded-checking circuit 124. Based on the judgement markreproduction signal, the recorded/unrecorded-checking circuit 124determines whether or not the address tracks 113 associated with thejudgement pits 133, 134 are to be made continuous storage areas 114.

To make an address track 113 a continuous storage area 114, therecorded/unrecorded-checking circuit 124 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to make the associated address track 113 a continuous storagearea 114.

Meanwhile, to not make an address track 113 a continuous storage area114 (to make the address track 13 unrecorded), therecorded/unrecorded-checking circuit 124 fees anaddress-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data.

As mentioned in the foregoing, as to the optical disk 131 of the presentembodiment, it can be immediately determined owning to the judgementpits 133, 134 in the judgement mark area 132 whether to make an addresstrack 113 in the address area 104 a continuous storage area 114.Therefore, the processing velocity of the optical-disk-read/writeapparatus 31 can be increased without reading the address track 113 inthe address area 104, i.e., address information.

Embodiment 6

The following will describe another embodiment of the present inventionin reference to FIGS. 28-31.

As shown in FIG. 28, an optical disk 141 of the present embodiment isreadable/writeable on both a groove 142 and a land 143 which are formedalternately as viewed along a diameter of the optical disk 141 in thenon-address area 105. The groove 142 and land 143 are spiral andrecording marks 111 are formed on the groove 142 and land 143 byprojection of a light beam 12.

The address area 104 is made up of a first address area 144 and a secondaddress area 145 which are adjacent to each other along tracks. In thefirst address area 144 constituting a head part of the address area 104,there are formed first address pits 146 along imaginary lines extendingfrom the groove 142. In the second address area 145 constituting thetail part of the address area 104, there are formed second address pits147 along imaginary lines extending from the land 143. Relativelyshifting the positions of the first address area 144 and the secondaddress area 145 along the tracks so that they do not overlap in adirection normal to the tracks eliminates crosstalk in signalsreproduced from the first and second address pits 146, 147. Thepositions of the first address area 144 and the second address area 145may be reversed.

In addition, some of the address tracks 113 in the address area 104extend from the groove 142, while the others extend from the land 143.In the present embodiment, those address track 113 extending from thegroove 142 are made continuous storage areas 114. In addition, theaddress track 113 is formed in both the first address area 144 and thesecond address area 145. Those address tracks 113 extending from thegroove 142 have the first address pits 146 in the first address area144, and those extending from the land 143 have the second address pits147 in the second address area 145.

As mentioned in the foregoing, as to an optical disk 141 of the presentembodiment, continuous storage areas 114 are formed in those addresstracks 113 extending from the groove 142, that is, in the first addressarea 144 and the second address area 145 of the address track 113.Therefore, like the foregoing optical disks 101, 131, to read/write thesecond storage layer 8, the sum of the areas of the recording marks 111included in the area of the beam spot 115 in the non-address area 105 onthe first storage layer 10 is substantially equal to the sum of thecontinuous storage areas 114 included in the area of the beam spot 115in the address area 104.

Thus, the intensity of the light beam 12 f projected onto the secondstorage layer 8 after passing through an address area 104 on the firststorage layer 10 can be made substantially equal to the intensity of thelight beam 12 e projected onto the second storage layer 8 after passingthrough the non-address area 105 on the first storage layer 10. As aresult, as to the optical disk 141 employing a lumped address scheme,the light beam intensity on the second storage layer 8 can be retainedat a substantially constant value regardless of whether the light is thelight beam 12 e passing through the non-address area 105 on the firststorage layer 10 or the light beam 12 f passing through the address area104 on the first storage layer 10, enabling stable and desirableread/write on the second storage layer 8.

In the present embodiment, the continuous storage area 114 is supposedto be formed in those address tracks 113 which extend from the groove142. The present embodiment is not limited by this: the continuousstorage area 114 may be formed in those address tracks 113 which extendfrom the land 143.

In addition, as in previous cases, the continuous storage area 114 maybe formed prior to the shipment of the optical disk 141 or by using theoptical-disk-read/write apparatus 31 after shipment. If theoptical-disk-read/write apparatus 31 is used to from an continuousstorage area 114, the aforementioned methods are all applicable.

Further, to form a continuous storage area 114, the signal processingand controlling unit 35 may have a land/groove determining circuit 125and the illuminating-unit-controlling circuit 122 as shown in FIG. 29.In this arrangement, for example, it is determined whether the trackcurrently being scanned is the groove 142 or the land 143, and thoseaddress tracks 113 which extend from either the groove 142 or the land143 in the address area 104 are made continuous storage areas 114according to a result of the determination.

In the arrangement, the land/groove determining circuit 125 determineswhether the track currently being scanned is the groove 142 or the land143 from a tracking servo signal or an address information reproductionsignal. If the determination turns out that it is the groove 142, theland/groove determining circuit 125 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122 to make an address track 113 acontinuous storage area 114. Upon receiving the signal, theilluminating-unit-controlling circuit 122 controls the illuminating unitso as to make an address track 113 which extends from the groove 142 acontinuous storage area 114.

Meanwhile, if the determination turns out that it is the land 143, therecorded/unrecorded-checking circuit 124 feeds anaddress-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data.

In addition, as to the optical disk 141, as shown in FIG. 30, thecontinuous storage area 114 may be formed in the second address area 145in those address tracks 113 which extend from the groove 142, in thefirst address area 144 in those address tracks 113 which extend from theland 143, and in each address track 113. The first address area 144 andthe second address area 145 may be reversed in position. Further, thecontinuous storage area 114 may be formed only at places where the firstaddress pit 146 and the second address pit 147 are provided, converselyto the formation places in FIG. 30.

In the arrangement, like the foregoing cases, the intensity of the lightbeam 12 f projected onto the second storage layer 8 after passingthrough an address area 104 on the first storage layer 10 can be madesubstantially equal to the intensity of the light beam 12 e projectedonto the second storage layer 8 after passing through the non-addressarea 105 on the first storage layer 10. As a result, as to anarrangement employing a lumped address scheme, the light beam intensityon the second storage layer 8 can be retained at a substantiallyconstant value, enabling stable and desirable read/write on the secondstorage layer 8.

Likewise, the continuous storage area 114 may be formed in advance,before the optical disk 141 is shipped or by using theoptical-disk-read/write apparatus 31 when the optical disk 141 is loadedinto the optical-disk-read/write apparatus 31. The aforementionedmethods are all applicable in these cases. For example, the continuousstorage area 114 may be formed based on reproduced address informationor whether the track being scanned is the groove 142 or the land 143.

To implement the actions, the signal processing and controlling unit 35in the optical-disk-read/write apparatus 31 is equipped with, forexample, an address-information-presence-checking circuit 126 and theilluminating-unit-controlling circuit 122 as shown in FIG. 31.

In the arrangement, the signal processing and controlling unit 35 feedsan address information signal reproduced from the address area 104 tothe address-information-presence-checking circuit 126 where theaddress-information-presence-checking circuit 126 determines whether theinput signal is carrying address information.

If the determination turns out that no address information is present,the address-information-presence-checking circuit 126 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122 to make an area where addressinformation is missing for the address track 113, that is, an area ofthe first address area 144 or the second address area 145, a continuousstorage area 114. Upon receiving that signal, theilluminating-unit-controlling circuit 122 controls the illuminating unitso as to form a continuous storage area 114 in an area where there is noaddress information for the address track 113.

Meanwhile, if address information is present, theaddress-information-presence-checking circuit 126 controls theilluminating unit and reads the address track 113 at a laser intensitywhich is incapable of recording data, so that no continuous storage area114 is formed in an area where address information is present for theaddress track 113.

In this and foregoing embodiments, if the optical-disk-read/writeapparatus 31 is used to form the continuous storage area 114 on anoptical disk, the cost of the optical disk can be reduced by reducingthe manufacturing steps of the optical disk.

In addition, in this and foregoing embodiments, the optical disks weresupposed to be high-to-low phase change types of storage media such thatthe interval areas between recording marks 111 exhibit a higherreflectance, i.e., a lower transmittance, than the recording mark 111 inthe first storage layer 10 and the second storage layer 8. The foregoingarrangements are applicable even when the optical disks are low-to-highphase change types of storage media such that the interval areas exhibita lower reflectance, i.e., a higher transmittance, than the recordingmarks 111.

Embodiment 7

The following will describe an embodiment of the present invention inreference to FIG. 62 and FIG. 63.

Referring to FIG. 63, an optical disk (optical storage medium) 201 ofthe present embodiment has a center hole 202 at its center and arecordable area 203 outside the center hole 202 in relation to adiameter. As shown in FIG. 35 and FIG. 36, in the recordable area 203, aspiral (or concentric) read/write guiding groove G is formed in aguiding-groove-and-pits-formed layer 212 and aguiding-groove-and-pits-formed intermediate layer 214 along whichinformation can be read/written. In addition, an innermost part 204 isformed around the center hole 202 and an outermost part 205 is formednear the circumference of the optical disk 201.

The optical disk 201 has prepit areas 206 made up of an inner prepitarea 206 a and an outer prepit area 206 b. The inner prepit area 206 ais provided adjacently outside the innermost part 204, and the outerprepit area 206 b is provided adjacently inside the outermost part 205.As shown in FIG. 37, in the prepit area 206, pits P are arranged forminga spiral (or concentric circles) in the guiding-groove-and-pits-formedlayer 212 and the guiding-groove-and-pits-formed intermediate layer 214.Prepit information is read from the pit row of the pits P. In the pitrow, typically, the writing power, reading power, and other kinds ofinformation on the optical disk 201 is prerecorded in the concave orconvex form (not shown) of the pits P.

As shown in FIG. 34 which is a vertical cross-sectional view of theoptical disk 201, the optical disk 201 is structured from theguiding-groove-and-pits-formed layer 212, a second storage layer (lastdata storage layer) 213, the guiding-groove-and-pits-formed intermediatelayer 214, a first storage layer (light-striking-side storage layer)215, and a surface-coating layer 216, with the layers sequentiallystacked on a disk substrate 211. To read/write the first storage layer215 and the second storage layer 213 on the optical disk 201, a lightbeam 217 projected from one side of the disk, i.e., the side on whichthe surface-coating layer 216 exists, is concentrated on the first andsecond storage layers 215, 213.

FIG. 35 shows the arrangement of the optical disk 201 in more detail. InFIG. 35, the disk substrate 211 is made of, for example, a 1.2-mm thick,transparent polycarbonate substrate. The guiding-groove-and-pits-formedlayer 212 is made of, for example, a 20-micron thick,ultraviolet-ray-setting resin layer and formed, for example, by apattern transfer technology termed 2P method. On one of the surfaces ofthe guiding-groove-and-pits-formed layer 212 which is closer to thesecond storage layer 213, the guiding groove G is provided in therecordable area 203 and the pits P (not shown in FIG. 35) are providedin the prepit area 206.

The second storage layer 213 includes, for example, an AlTi-alloyreflective film 213 a, a ZnS—SiO₂ interference film 213 b, a SiNprotective film 213 c, a GeSbTe phase change recording layer 213 d, aSiN protective film 213 e, and a ZnS—SiO₂ interference film 213 f. Thesefilms are formed as they are sequentially deposited on theguiding-groove-and-pits-formed layer 212 by means of sputtering.

Like the guiding-groove-and-pits-formed layer 212, theguiding-groove-and-pits-formed intermediate layer 214 is made of, forexample, a 20-micron thick, ultraviolet-ray-setting resin layer andformed by, for example, a pattern transfer technology termed 2P method.On one of the surfaces of the guiding-groove-and-pits-formedintermediate layer 214 which is closer to the first storage layer 215,the guiding groove G is provided in the recordable area 203 and the pitsP (not shown in FIG. 35) are provided in the prepit area 206.

Like the second storage layer 213, the first storage layer 215 includesfor example, a ZnS—SiO₂ interference film 215 a, a SiN protective film215 b, a GeSbTe phase change recording layer 215 c, a SiN protectivefilm 215 d and a ZnS—SiO₂ interference film 215 e. The first storagelayer 215 is formed by sequentially depositing these films on theguiding-groove-and-pits-formed intermediate layer 214 by means ofsputtering.

The surface-coating layer 216 is made of, for example, a 80-micronthick, ultraviolet-ray-setting resin layer, and formed by spin coatingthe first storage layer 215 with an ultraviolet-ray-setting resin andsetting the resin by the projection of ultraviolet rays.

The optical disk substrate 211 is, as mentioned in the foregoing, asubstrate made of a transparent polycarbonate. However, when a lightbeam 217 is incident to the surface-coating layer 216 as is the casewith the optical disk 201 of the present embodiment, the disk substrate211 does not need be transparent, and may be an opaque, metallicsubstrate.

In addition, the optical disk 201 of the present embodiment is providedwith the guiding-groove-and-pits-formed layer 212 and theguiding-groove-and-pits-formed intermediate layer 214 which are formedby 2P method and which have the guiding groove G and the pits P.However, a disk substrate 211 provided on its surface directly with aguiding groove G and pits P may be formed by, for example, injectionmolding. The structure including the disk substrate 211 does not requirethe guiding-groove-and-pits-formed layer 212 and theguiding-groove-and-pits-formed intermediate layer 214.

In addition, although the surface-coating layer 216 is formed on thefirst storage layer 215 by spin coating, the layer 216 may be providedinstead in the form of uniformly thick, transparent sheet pasted on thefirst storage layer 215.

In addition, the optical disk 201 has a structure including theguiding-groove-and-pits-formed layer 212, the second storage layer 213,the guiding-groove-and-pits-formed intermediate layer 214, the firststorage layer 215, and the surface-coating layer 216 sequentiallystacked on the optical disk substrate 211. This is not the only optionavailable. For example, the optical disk 201 may be structured so thatit includes the guiding-groove-and-pits-formed layer 212, the firststorage layer 215, the guiding-groove-and-pits-formed intermediate layer214, the second storage layer 213, and the surface-coating layer 216sequentially stacked on the optical disk substrate 211, with the lightbeam 217 projected onto the optical disk substrate 211 as shown in FIG.38. In this structure, the films constituting the first storage layer215 and the second storage layer 213 are in the reverse order to thoseshown in FIG. 35.

An optical-disk-read/write apparatus (optical read/write apparatus)which reads/writes on the optical disk 201 was, as with the optical disk1, described in reference to FIG. 5.

In the present embodiment, the optical-disk-read/write apparatus 31reads from, or writes into, the second storage layer 213 after therecordable area 203 of the first storage layer 215 is fully recorded.The operations in this case are carried out under the control of thesignal processing and controlling unit 35 on the optical system unit(illuminating means) 34 and the slide driving unit (illuminating means).

In the foregoing situation, the following will describe how theoptical-disk-read/write apparatus 31 reads/writes on the optical disk201, supposing that data is recorded in the first storage layer 215 ofthe optical disk 201, starting with the inner prepit area 206 a in therecordable area 203 until data fills part of the recordable area 203 ofthe first storage layer 215, and then the operation moves toreading/writing in the second storage layer 213. It is also supposedthat the optical disk 201 is a high-to-low medium such that the intervalarea is more reflective than the recording mark area and data isrecorded by phase change.

As a result of recording in the first storage layer 215, as shown inFIG. 39 and FIG. 40, a recorded part 203 a 1 (shown by hatched lines) isproduced covering the inner prepit area 206 a of the recordable area 203of the first storage layer 215 up to partway of the recordable area 203.

Here, the first storage layer 215 is more optically transmissive than inthe recorded part 203 a 1 than other areas. As a result, the light beam217 projected on the second storage layer 213 is more intense when it isconcentrated on the second storage layer 213 if the light beam 217(light beam 217 b) has passed through the recorded part 203 a 1 than ifthe light beam 217 (light beam 217 a) has passed through an area otherthan the recorded part 203 a 1 (non-recorded area). In other words, inrecording data into the second storage layer 213, the light beam 217varies in intensity when it reaches the second storage layer 213 afterpassing through the first storage layer 215, depending on whether it hascome through the recorded part 203 a 1. In this case, to record datainto the second storage layer 213, a complex write system is requiredwhich can vary the light beam 217 in intensity depending on whetherthere are any records stored in the first storage layer 215.

A similar difference develops in intensity of the light beam 217, and asimilarly complex read system is required when data is read from thesecond storage layer 213, because the return light reflected off thesecond storage layer 213 changes in quantity depending on whether thelight beam 217 has passed through the recorded part 203 a 1 of the firststorage layer 215.

Accordingly, in the optical-disk-read/write apparatus 31 of the presentembodiment, as shown in FIG. 41, data is read/write from/into the secondstorage layer 213 only after the recordable area 203 of the firststorage layer 215 is fully recorded. In other words, to record on theoptical disk 201, the optical-disk-read/write apparatus 31 first writesdata in the first storage layer 215, and only after the recordable area203 of the first storage layer 215 is recorded to its full capacity,starts writing or reading data into/from the second storage layer 213.

The operation ensures that in the read/write operation as to the secondstorage layer 213, the light beam 217 projected on the second storagelayer 213 always passes through the fully recorded, first storage layer215 before entering the second storage layer 213. In both read and writeoperations, the light beam 217 has a constant intensity when it reachesthe second storage layer 213, which eliminates the need to use a complexread/write system to control the intensity of the light beam 217. Stableread/write operations are thus achieved.

FIG. 62 shows the first storage layer 215 and the second storage layer213 near the periphery of the optical disk 201 in their initial states.On the optical disk 201, the first storage layer 215 has an unrecordedrecordable area 203 a and a blank area 205 a constituting the outermostpart 205, and the second storage layer 213 has an unrecorded recordablearea 203 b, an outer prepit area 206 a, and a blank area 205 bconstituting the outermost part 205. In this situation, the blank areas205 a, 205 b are those areas where no guiding groove G or pits P areformed. The innermost part 204 of the first and second storage layers215, 213 also has similar blank areas (not shown).

The optical disk 201 in this state exhibits uniform transmittance, sincethe recordable area 203 a of the first storage layer 215 is unrecorded.Therefore, when prepit information is reproduced by concentrating thelight beam 217 on the outer prepit area 206 b of the second storagelayer 213, the intensity of the reproduction signal does not vary. Inaddition, since the prepit area 206 is provided to the second storagelayer 213, the second storage layer 213 is stably readable/writeablewithout being affected by the prepit area 206.

Next, as shown in FIG. 42, writing in a part of the unrecordedrecordable area 203 a produces a recorded part 203 a 1 and leaves theother part as a non-recorded part 203 a 2. In this case, as shown inFIG. 43, in the recorded part 203 a 1, recording marks M with reducedtransmittance are formed in the guiding groove G. In the non-recordedpart 203 a 2, no recording marks M are formed and the transmittanceremains unchanged. Therefore, the light beam 217 c having passed throughthe recorded part 203 a 1 differs in intensity from the light beam 217 dhaving passed through the non-recorded part 203 a 2. The reproductionsignal of prepit information therefore differs in intensity between thelight beams 217 c and 217 d.

In addition, as to the optical disk 201, typically, it is impossible tocompletely match the center of the spiral guiding groove G on the firststorage layer 215 and the center of the spiral pit row on the secondstorage layer 213. Therefore, when the light beam 217 e illuminates botha part of the recorded part 203 a 1 and a part of the non-recorded part203 a 2 before being concentrated on the outer prepit area 206 b of thesecond storage layer 213 as shown in FIG. 42, the boundary between therecorded part 203 a 1 and the non-recorded part 203 a 2 moves in thelight beam 217 e with the rotation of the optical disk.

Therefore, as shown in FIG. 44, the reproduction signal of the prepitinformation varies in intensity as the optical disk 201 rotates. FIG. 44only shows the envelope E of the reproduction signal; the intensity ofthe reproduction signal is shown on the axis of ordinates and theangular position of the rotating optical disk 201 is shown on the axisof abscissas. FIG. 45 shows with the angle axis enlarged thereproduction signal S1 of prepit information at the 0-degree angularposition of FIG. 44 and the reproduction signal S2 of prepit informationat the 180-degree angular position of FIG. 44. To convert thereproduction signals S1, S2 into digital signals, detection needs tocarried out with the slice levels set to the mean levels to of thereproduction signals S1, S2. However, comparing the reproduction signalS1 with the reproduction signal S2 will show that the mean levels differgreatly, which makes it impossible to carry out detection using a singleslice level.

The problem can be solved by detecting the upper envelope E1 and lowerenvelope E2 which constitute the envelope E of the reproduction signaland setting the variable slice level Lv to their mean levels as shown inFIG. 46. FIG. 47 shows the configuration of a reproduction circuitproducing a digital signal from the slice level Lv.

The reproduction circuit includes an envelope detecting circuit 251, aslice level producing circuit 252, and a comparator 253.

The envelope detecting circuit 251 as envelope detecting means is madeof, for example, a peak-hold circuit and a bottom-hold circuit; thepeak-hold circuit detects the upper envelope E1 and the bottom-holdcircuit detects the lower envelope E2.

The slice level producing circuit 252 as mean level producing meansproduces a slice level Lv by outputting a mean value of values of thedetected upper and lower envelopes E1, E2. The slice level producingcircuit 252 is made of, for example, an operation circuit including anadder circuit for adding the values of the envelopes E1, E2 and adivider circuit for dividing the sum by 2.

The comparator 253 as digital converting means compares the reproductionsignal with the slice level Lv produced by the slice level producingcircuit 252 and converts the reproduction signal to a binary digitalsignal. For example, the comparator 253 produces a 1 for output when thereproduction signal is above the slice level Lv and a 0 for output whenthe reproduction signal is below the slice level Lv.

In the reproduction circuit thus configured, the reproduction signal isfed to the envelope detecting circuit 251 and the comparator 253. Theenvelope detecting circuit 251 detects the upper envelope signal E1 andthe lower envelope E2 of the reproduction signal. The slice levelproducing circuit 252 produces slice levels Lv from the envelope E1, E2.The comparator 253 produces a digital signal by comparing thereproduction signal with the slice level Lv.

In addition, FIG. 48 shows the relationship between the reproductionsignal intensity and the angular position of the optical disk 201, as tothe method to produce a digital signal from a reproduction signal bymeans of the reproduction circuit shown in FIG. 49. The reproductioncircuit in FIG. 49 includes a high-pass filter 261, a slice levelproducing circuit 262, and a comparator 263.

The high-pass filter 261 as low frequency variation removing meansremoves low frequency variations from a reproduction signal and passeshigh frequency components. The slice level producing circuit 262produces a slice level of a constant voltage. The comparator 263 asdigital converting means compares the reproduction signal transmittedthrough the high-pass filter 261 to the slice level as is the case withthe comparator 253 and converts into binary digital signal.

In the reproduction circuit thus configured, the incoming reproductionsignal is first stripped of its low frequency variations by thehigh-pass filter 261. The reproduction signal, before being fed to thehigh-pass filter 261, includes low frequency variations, and thereforethe mean level of the envelope E changes as shown in FIG. 46. However,the reproduction signal is past through the high-pass filter 261, andthe mean level of the envelope E becomes constant regardless of theangle as shown in FIG. 48.

The comparator 263 compares the reproduction signal past through thehigh-pass filter 261 with the constant slice level Lc fed from the slicelevel producing circuit 262 and produces a digital signal.

Although the reproduction circuit and the slice level producing circuit262 produce the slice level Lc in the foregoing, the slice level Lc maybe set to 0 volts, because the mean levels of the upper envelope E1 andthe lower envelope E2 are normally equal to 0 volts as the reproductionsignal passes through the high-pass filter 261. Therefore, in this case,the slice level producing circuit 262 can be omitted.

As described in the foregoing, the provision of the prepit area 206 inthe second storage layer 213 enables the optical disk 201 to read/writedata from/into the second storage layer 213 without changing theread/write sensitivity of the recordable area 203. In addition, the useof the reproduction circuit shown in FIG. 47 or FIG. 49 ensures that adigital signal is derived stably from a reproduction signal, even if thereproduction signal of prepit information varies in intensity with therotation of the optical disk 201 provided that the light beam 217 eilluminates both the recorded part 203 a 1 and the non-recorded part 203a 2 before being focused on the outer prepit area 206 b of the secondstorage layer 213.

However, as mentioned earlier, the non-recorded part 203 a 2 exhibits alower transmittance than the recorded part 203 a 1. When data is to beread from the prepit area 206 including the outer prepit area 206 busing the light beam 217 d traveling through the non-recorded part 203 a2 of the first storage layer 215, as could be understood from FIG. 46and FIG. 48, the reproduction signal has so small an amplitude that theprepit information cannot be reproduced stably. Accordingly, preferably,the part of the first storage layer 215 through which the light beam 217e is transmitted is fully recorded and thus exhibits a relatively hightransmittance.

FIG. 50 shows a structure of the optical disk 201 capable of increasingthe amplitude of the reproduction signal obtained from prepit area 206(not shown except the outer prepit area 206 b) on the second storagelayer 213.

The optical disk 201 has a pseudo-recording area 207 interposed betweenthe recordable area 203 a and the blank area 205 a. The pseudo-recordingarea 207 is provided in a part of the first storage layer 215 whichcorresponds to the prepit area 206 of the first storage layer 215 andstores pseudo information in advance. In the pseudo-recording area 207,as in the recordable area 203, the transmittance lowers where recordingmarks M are formed in the guiding groove G as shown in FIG. 51. Thus,the pseudo-recording area 207 has as high a transmittance as therecordable area 203, and the light beam 217 passing through thepseudo-recording area 207 comes to have a high intensity. Thus, theamplitude of the reproduction signal of the prepit area 206 on thesecond storage layer 213 can be increased.

The recording marks M formed on the pseudo-recording area 207 differfrom those formed on the recordable area 203; the former include no mainrecording information, but pseudo recording information. As pseudorecording information, no particular information needs be recorded, butnonsense or meaningless information may be recorded. Alternatively, ifthe pseudo-recording area 207 is to be formed in advance prior to theshipment of the optical disk 201, identification information, encryptioninformation, and other kinds of information may be recorded in thepseudo-recording area 207 which is unique to individual optical disks201.

In this situation, as shown in FIG. 50, preferably, the pseudo-recordingarea 207 is formed so that the light beams 217 f, 217 g always travelthrough the pseudo-recording area 207 of the first storage layer 215even when data is read from the edges of the prepit area 206 b of thesecond storage layer 213 in relation to the radius direction of thedisk. Accordingly, the pseudo-recording area 207 is provided covering awider area than the outer prepit area 206 b of the second storage layer213.

For example, supposing the first storage layer 215 is separated from thesecond storage layer 213 by a distance of 20 microns, the light beam 217focused on the second storage layer 213 forms on the first storage layer215 a spot having a radius of about 10 microns. Therefore, thepseudo-recording area 207 needs be formed at least about 10 micronswider than both ends of the prepit area 206 of the second storage layer213. In addition, when the center of the guiding groove G formed on thefirst storage layer 215 does not match the center of the pit row formedon the second storage layer 213, hence eccentricity exists between thetwo centers, the pseudo-recording area 207 needs be widened by an amountequivalent to the eccentricity. For this reason, the pseudo-recordingarea 207 is preferably formed about 100 microns wider than both ends ofthe prepit area 206 of the second storage layer 213.

FIG. 50 shows an example in which the pseudo-recording area 207 isprovided in the outer prepit area 206 b. A similar pseudo-recording areamay be provided in the inner prepit area 206 a too.

In this situation, the pseudo-recording area 207 may be either formedprior to the shipment of the optical disk 201 or formed by theoptical-disk-read/write apparatus 31 when an unused optical disk 201 isloaded in the optical-disk-read/write apparatus 31 for replay orrecording. The provision of the pseudo-recording area 207 using anoptical-disk-read/write apparatus eliminates the need to provide thepseudo-recording area 207 prior to the shipment of the optical disk,which enables reduction of the cost of the optical disk.

FIG. 52 shows a configuration of pseudo recording circuit provided inthe optical-disk-read/write apparatus 31 to form a pseudo-recording area207. The configuration includes the aforementionedpseudo-recording-status-checking circuit 271 in the signal processingand controlling unit 35.

The pseudo-recording-status-checking circuit 271 as recording statuschecking means checks, based on the reproduction signal produced by alight-receiving element 47 from the reflection off the pseudo-recordingarea 207, whether the pseudo-recording area 207 already contains pseudorecording information. The pseudo-recording-status-checking circuit 271includes a comparator and other circuits to check and determine whetherthe pseudo-recording area 207 contains any records, in accordance withwhether or not the reproduction signal which represents the quantity oflight reflected off the pseudo-recording area 207 exceeds apredetermined threshold value.

In the arrangement, the pseudo-recording area 207 is read immediatelyafter the optical disk 201 is loaded in the optical-disk-read/writeapparatus 31. The pseudo-recording-status-checking circuit 271 checksbased on the reproduction signal whether the pseudo-recording area 207is fully recorded or not.

If the pseudo-recording area 207 is not fully recorded, thepseudo-recording-status-checking circuit 271 regards the optical disk201 as being never used, and feeds a pseudo writing-instruction signalto the illuminating-unit-controlling circuit 36 as pseudo-recordingmeans provided in the signal processing and controlling unit 35. As aresult, pseudo information is recorded in the pseudo-recording area 207of the first storage layer 215 under the control of theilluminating-unit-controlling circuit 36. Meanwhile, if thepseudo-recording area 207 is fully recorded, thepseudo-recording-status-checking circuit 271 regards the loaded opticaldisk 201 as having been used, and feeds an ordinary writing-instructionsignal to the illuminating-unit-controlling circuit 36. As a result, anordinary recording operation is performed as to the optical disk 201under the control of the illuminating-unit-controlling circuit 36.

Next, the following description will describe an optical disk 201 inwhich the first storage layer 215 has a prepit area 206. As acomparative example, an optical disk 281 is first described with whichno consideration is given to the read/write sensitivity of the secondstorage layer 215.

With the optical disk 281, as shown in FIG. 53, a blank area 205 a ofthe first storage layer 215 is provided in the same range as a blankarea 205 b of the second storage layer 213. In the first storage layer215, an outer prepit area 206 b is provided between the recordable area203 a and the blank area 205 a. In addition, an inner prepit area 206 a(not shown) is also provided on the first storage layer 215.

Since the prepit area 206 is located on the light-striking side of theoptical disk 281 thus structured, the reproduction signal derived fromthe prepit area 206 never varies in intensity. The optical disk 281 isfree from the problem that the reproduction signal derived from theprepit area 206 varies in intensity as shown in FIG. 42. However, theprovision of the prepit area 206 on the first storage layer 215 causesthe same problem as with the conventional optical disk (see FIG. 70).Concretely, the first storage layer 611 exhibits different opticaltransmittances between the recordable area 603 and the prepit area 606,resulting in variations in read/write sensitivity of the second storagelayer 612. Now, the variations in recording sensitivity of the opticaldisk 281 are elaborately described.

As to the optical disk 281, the recordable area 203 a of the firststorage layer 215 is first fully recorded by a recording operation ofthe optical-disk-read/write apparatus 31. In this situation, the fullyrecorded, recordable area 203 a includes high-transmittance recordingmarks M, and the light beam 217 h concentrated on the second storagelayer 213 after passing through the recordable area 203 a exhibits arelatively high intensity. Meanwhile, the light beam 217 i concentratedon the second storage layer 213 after passing through the prepit area206 with no recording marks M exhibits a relatively low intensity.

Next, to record data in the recordable area 203 b of the second storagelayer 213, the light beam 217 h and the light beam 217 i, althoughoriginally of the same intensity, differs in intensity when they reachthe second storage layer 213. Therefore, the recording sensitivityvaries depending upon where recording takes place, which makes itextremely difficult to perform stable recording. Further, if a lightbeam passes through a boundary between the fully recorded recordablearea 203 a and the prepit area 206 before concentrated on the secondstorage layer 213, since there exists eccentricity which is defined asthe displacement in position between the center of the guiding groove Gon the first storage layer 215 and the center of the guiding groove G onthe second storage layer 213, the recording sensitivity undesirablyvaries with rotation of the optical disk 281.

By contrast, the optical disk 201 shown in FIG. 54 provides means tosolve these problems by expanding the blank area 205 b. The followingwill describe such an optical disk 201.

As to the optical disk 201 shown in FIG. 54, the blank area 205 b thesecond storage layer 213 is expanded inwards, and a light beam 217 jentering the optical disk 201 always passes through the fully recordedrecordable area 203 a of the first storage layer 215 before concentratedon the second storage layer 213. In this manner, as to the optical disk201, the recordable area 203 a of the first storage layer 215 is formedwider than the recordable area 203 b of the second storage layer 213,and the prepit area 206 is formed along the outer circumference of therecordable area 203 a. The configuration makes the intensity of thelight beam 217 j always constant on the second storage layer 213 andthus achieves stable recording to the second storage layer 213 andstable reproduction of prepit information from the first storage layer215.

Now, it will be described how much wider the recordable area 203 a ofthe first storage layer 215 should be than the recordable area 203 b ofthe second storage layer 213. Assuming that the first storage layer 215is separated from the second storage layer 213 by a distance of 20microns, the light beam 217 j focused on the second storage layer 213forms on the first storage layer 215 a spot having a radius of about 10microns. Therefore, the recordable area 203 b needs be formed at leastabout 10 microns wider than the width of the recordable area 203 a. Inaddition, when the center of the guiding groove G formed on the firststorage layer 215 does not match the center of the guiding groove Gformed on the second storage layer 213, hence eccentricity existsbetween the two centers, the recordable area 203 a needs be widened byan amount equivalent to the eccentricity. Therefore, in this case, therecordable area 203 a is preferably formed about 100 microns wider thanthe width of the recordable area 203 b.

As to the optical disk 201, the recordable area 203 b of the secondstorage layer 213 narrows down and the storage capacity decreases. Bycontrast, the optical disk 201 shown in FIG. 55 and FIG. 56 has such astructure to add to the storage capacity while preventing the prepitarea 206 from reducing the recording sensitivity.

The optical disk 201 has in place of the aforementioned prepit area 206a prepit area 208 made of an inner prepit area 208 a and an outer prepitarea 208 b, as shown in FIG. 55. The prepit area 208 has an opticaltransmittance which is equal to that of the fully recorded recordablearea 203 a of the first storage layer 215 shown in FIG. 56.

As shown in FIG. 57, in the prepit area 208, alternate pit rows of pitsP which are spirally (or concentrically) arranged have a continuouslyrecorded, continuous storage area R. In the continuous storage area R,the pits P and the intervals between the pits P are continuously in thesame state, i.e., have the same transmittance, as the recording marks Min the recordable area 203 a.

In the recorded recordable area 203 a, a fully recorded portion(recording mark M) and a non-fully-recorded portions are formedalternately in the guiding groove G. In practice, the lengths of thefully recorded and non-fully-recorded portions along the guiding grooveG alters depending on recording information. However, as to the guidinggroove G, recording is done so that the recorded portions and thenon-fully-recorded portions are formed at a substantially equal ratio.In addition, the depression area (land area) between any adjacentguiding grooves G are non-recorded areas and formed substantially aswide as the guiding groove G. Therefore, the sum of the areas of therecording marks M is equal to ¼ the net area of the recordable area 203a.

Meanwhile, in the prepit area 208, the non-recorded area between anyadjacent pit rows is formed substantially as wide as the diameter of thepit P. Therefore, to form a recorded portion (¼ the net prepit area 208)which has an area substantially equal to the recorded portion of therecordable area 203 a, recording needs be done so that a continuousstorage area R can be formed for alternate pit rows.

Other than guiding groove recording schemes, to employ a land and grooverecording scheme whereby recording marks M are formed not only in theguiding groove G, but also in land areas, the sum of the areas of therecording marks M formed in the recordable area 203 a is ½ the net areaof the recordable area 203 a. Therefore, to form a recorded portionhaving an area substantially equal to the recorded portion (½ the netarea of the prepit area 208) of the recordable area 203 a, recordingneeds be done so that a continuous storage area R can be formedcontinuously along a pit row.

As mentioned in the foregoing, the continuous storage area R exhibits ashigh an optical transmittance as the recording mark M. Therefore, asshown in FIG. 58, the fully recorded portions formed on the firststorage layer 15 in the spots of a light beam 217 k passing through thefully recorded recordable area 203 a before being concentrated on thesecond storage layer 213 and a light beam 217 l passing through theouter prepit area 208 b before being concentrated on the second storagelayer 213 have the substantially equal areas. This makes the intensitiesof the light beams 217 k, 217 l on the second storage layer 213substantially equal, and the second storage layer 213 no longer variesin recording sensitivity even when the prepit area 208 is provided.Therefore, expanding the recordable area 203 b of the second storagelayer 213 adds to the storage capacity as compared to the optical disk201 in FIG. 54.

In this situation, the blank areas 205 a, 205 b are unrecorded andexhibit low optical transmittance. The ends of the recordable area 203 bof the second storage layer 213 therefore need be determined so that thelight beam 217 l reaching the second storage layer 213 always passesthrough the outer prepit area 208 b, as shown in FIG. 56.

In this manner, as to the optical disk 201, in the prepit area 208 ofthe first storage layer 215, alternate pit rows have a continuousstorage area R, and the outer periphery of the outer prepit area 208 bis positioned further outside the outer periphery of the recordable area203 b of the second storage layer 213. In the case of the inner prepitarea 208 a, its inner periphery is positioned further inside the innerperiphery of the recordable area 203 b of the second storage layer 213.Thus, the light beams 217 k, 217 l always have equal intensities on thesecond storage layer 213. Therefore, data is stably written to thesecond storage layer 213, and the optical disk 201 comes to have afurther increased capacity.

Now, it will be described how much closer to the outer periphery theperiphery of the outer prepit area 208 b should be positioned than therecordable area 203 b. Assuming that the first storage layer 215 isseparated from the second storage layer 213 by a distance of 20 microns,the light beam focused on the second storage layer 213 forms on thefirst storage layer 215 a spot having a radius of about 10 microns.Therefore, the outer prepit area 208 b needs be formed so that itsperiphery is positioned at least about 10 microns closer to the outerperiphery than the periphery of the recordable area 203 b. Likewise, theinner prepit area 208 a needs be formed so that its periphery ispositioned at least about 10 microns closer to the inner periphery thanthe periphery of the recordable area 203 b.

Further, if the center of the guiding groove G on the first storagelayer 215 does not match the center of the guiding groove G on thesecond storage layer 213, and hence eccentricity exists, the outerprepit area 208 b needs be expanded by an amount equivalent to theeccentricity. In this case, the outer prepit area 208 b is preferablyformed so that its edges are positioned about 100 microns closer to theouter periphery than the edges of the recordable area 203 b. Preferably,the inner prepit area 208 a is formed likewise.

In this situation, the continuous storage area R may be formed in thepit row in the prepit area 208 either prior to the shipment of theoptical disk 201 or by using the optical-disk-read/write apparatus 31when an unused optical disk 201 is loaded into theoptical-disk-read/write apparatus 31. The formation of the continuousstorage area R using the optical-disk-read/write apparatus 31 eliminatesthe need to form the continuous storage area R prior to the shipment ofthe optical disk 201, and reduces the cost of the optical disk 201.

FIG. 59 shows a configuration to form a continuous storage area R in thepit row in the prepit area 208 using the optical-disk-read/writeapparatus 31 in the foregoing manner. The configuration includes theaforementioned continuous-storage-area-presence-checking circuit 291provided in the signal processing and controlling unit 35.

The continuous-storage-area-presence-checking circuit 291 as continuousstorage area checking means checks and determines based on thereproduction signal produced by the light-receiving element 47 from thereflection off the prepit area 208 whether the prepit area 208 containsa continuous storage area R as mentioned in the foregoing. Thecontinuous-storage-area-presence-checking circuit 291 includes acomparator and other circuits to check and determine whether thepseudo-recording area 207 contains any records, in accordance withwhether or not the reproduction signal which represents the quantity ofreflected light reflected off the prepit area 208 exceeds apredetermined threshold value.

In the arrangement, to check the presence of the continuous storage areaR, the prepit area 208 is read immediately after the optical disk 201 isloaded in the optical-disk-read/write apparatus 31. Here, a light beamis projected on the prepit area 208 for tracking under the control ofthe illuminating-unit-controlling circuit 36 in the signal processingand controlling unit 35. Here, the pit row acts as a tracking guidewhich is a rough equivalent to the guiding groove G.

When there is already formed a continuous storage area R, the quantityof light reflected off the prepit area 208 changes for alternate pitrows, and the reproduction signal representative of the quantity ofreflected light varies accordingly. In thecontinuous-storage-area-presence-checking circuit 291, as mentioned inthe foregoing, the varying reproduction signal is converted to a signalof a constant level by a low-pass filter and compared with apredetermined reference value by the comparator. In this case, thesignal is larger than the reference value, thecontinuous-storage-area-presence-checking circuit 291 regards the loadedoptical disk 201 as having been used and feeds an ordinarywriting-instruction signal to the illuminating-unit-controlling circuit36. As a result, under the control of the illuminating-unit-controllingcircuit 36, ordinary recording takes place on the optical disk 201.

Meanwhile, when there is formed no continuous storage area R, thequantity of light reflected off the prepit area 208 does not vary.Neither does the reproduction signal. Therefore, the signal havingpassed through the low-pass filter is smaller than the reference value,the continuous-storage-area-presence-checking circuit 291 regards theloaded optical disk 201 as being never used, and feeds acontinuous-recording-instructing signal to theilluminating-unit-controlling circuit 36 as continuous recording means.As a result, under the control of the illuminating-unit-controllingcircuit 36, recording takes place on the optical disk 201 so that acontinuous storage area R is formed in the prepit area 208.

So far, the description was limited only to the optical disk 201 withonly two data storage layers. Instead, the optical disk 201 may includethree or more data storage layers. The following will describe such anoptical disk 201 with three data storage layers.

In addition to a first storage layer 215 and a second storage layer 213,the optical disk 201 includes a third storage layer 218 as a last datastorage layer which is most distanced from a light-entering surface, asshown in FIG. 60. The prepit area 206 is provided not in the firststorage layer 215 or the second storage layer 213, but only in the thirdstorage layer 218, between a recordable area 203 c and a blank area 205c.

As to the optical disk 201, similarly to the optical disk 201 shown inFIG. 62, in reading data from a prepit area 206 in the third storagelayer 218 the quantity of light reflected off a prepit area 206 variesdepending upon whether the first storage layer 215 and the secondstorage layer 213 through which light beams 217 m, 217 n pass are fullyrecorded or not. However, a slice level can be produced from theenvelope of a reproduction signal by using the reproduction circuitshown in FIG. 47. Obtaining a digital signal with the slice level as areference, prepit information can be reproduced stably. In addition, byusing the reproduction circuit shown in FIG. 49, prepit information canbe reproduced stably by obtaining a digital signal by comparing with aconstant slice level a reproduction signal of the prepit area 206 fromwhich low frequency components are removed by a high-pass filter.

In this situation, in recording data on the optical disk 201, therecording on the second storage layer 213 is started after the firststorage layer 215 is fully recorded, and the recording on the thirdstorage layer 218 is started after the second storage layer 213 is fullyrecorded. In addition, in focusing a light beam on the second storagelayer 213, the light beam needs always be transmitted through a recordedarea 203 a of the first storage layer 215 so that a light beam ofconstant intensity reaches the second storage layer 213. To this end,the recordable area 203 a is formed wider than the recordable area 203 bboth on the inner and outer peripheries.

Next, as to the optical disk 201 shown in FIG. 61, the third storagelayer 218 has the prepit area 206, and the first storage layer 215 andthe second storage layer 213 have respective pseudo-recording areas 207a, 207 b where pseudo information is recorded. As to the optical disk201, the pseudo-recording areas 207 a, 207 b are formed at suchpositions that the light beams 217 m, 217 l focused on the prepit area206 of the third storage layer 218 are always transmitted through thepseudo-recording areas 207 a, 207 b before reaching the prepit area 206.

Using such an optical disk 201, similarly to the optical disk 201 shownin FIG. 50, due to relatively high optical transmittance of thepseudo-recording area 207 a, 207 b, the intensities of the light beams217 m, 217 n passing through the pseudo-recording areas 207 a, 207 b canbe maintained at high values. Therefore, it becomes possible to increasethe amplitude of the reproduction signal derived from the prepit area206 of the third storage layer 218 and eliminate the variations of thereproduction signal along the direction of the circumference.

The pseudo-recording areas 207 a, 207 b may be formed prior to theshipment of the optical disk 201 or using the optical-disk-read/writeapparatus 31 in the aforementioned manner.

Further, the optical disk 201 shown in FIG. 62 has the prepit area 206only in the first storage layer 215 which is located close to thelight-entering surface. Such an optical disk 201, since the prepit area206 is located close to the light-entering surface, is free fromvariations in the quantity of light reflected off the prepit area 206and its prepit information can be stably reproduced.

In addition, to eliminate variations from recording sensitivity,similarly to the case in FIG. 54, in reading or writing in therecordable area 203 b of the second storage layer 213, a light beam 217o needs to always pass through a fully recorded recordable area 203 a ofthe first storage layer 215 before reaching the second storage layer213; and in reading or writing in the third storage layer 218, a lightbeam 217 p needs to always pass through the fully recorded recordableareas 203 a, 203 b of the first storage layer 215 and the second storagelayer 213, respectively, before reaching the third storage layer 218. Tothis end, the recordable area 203 b is formed wider than the recordablearea 203 c and the recordable area 203 a is formed wider than therecordable area 203 b.

The optical disk 201 shown in FIG. 63 has the prepit area 208 (only theouter prepit area 208 b is shown) in place of the prepit area 206 in thefirst storage layer 215 of the optical disk 201 shown in FIG. 62. Theoptical disk 201, similarly to the optical disk 201 in FIG. 56, has: theprepit area 208 where the optical transmittance is high; the innerprepit area 208 a whose inner edge is positioned further inwards thanthe inner edges of the recordable areas 203 b, 203 c; and the outerprepit area 208 b whose outer edge is positioned further outwards thanthe outer edges of the recordable areas 203 b, 203 c.

This makes always constant the intensities of a light beam 217 rreaching the second storage layer 213 and the light beam 217 s reachingthe third storage layer 218. Therefore, it data is recorded stably inthe second storage layer 213 and the third storage layer 218, and theoptical disk, 201 is more capacious.

As described in the foregoing, an optical read/write apparatus of thepresent invention causes a read/write light beam from an illuminatingsection to strike only one side of an optical storage medium includingstacked data storage layers each of which is readable/writeableseparately from the other layers, and the apparatus includes acontrolling section for controlling the illuminating section so thatdata is read/written from/into a recordable area of a second datastorage layer after a recordable area of a first data storage layer isfully recorded, and the first data storage layer is one of the datastorage layers which is located closest to a light-striking surface ofthe medium, and the second data storage layer is another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

Further, an optical read/write method of the present invention causes aread/write light beam to strike only one side of an optical storagemedium including stacked data storage layers each of which isreadable/writeable separately from the other layers, and the methodincludes the step of reading/writing data from/into a second datastorage layer after fully recording a recordable area of a first datastorage layers which is located closest to a light-striking surface ofthe medium, and the second data storage layer is another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

According to the arrangement, after fully recording the recordable areaof the first data storage layer on the light-striking side, data isread/written from/into the second data storage layer which is locatednext to the first data storage layer, opposite the light-strikingsurface.

Therefore, when data is read/written from/into the second data storagelayer, substantially all the read/write light striking the second datastorage layer after passing through the first data storage layer passesthrough the recordable area of the first data storage layer that hasbeen recorded. Thus, even when an optical transmittance in therecordable area of the first data storage layer varies depending onwhether the recordable area holds any record or not, it is possible toilluminate light having uniform intensity to the substantially entirerecordable area of the second data storage layer. As a result, it ispossible to realize a desirable reading/writing property without using acomplex read/write system.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium and is arranged so as to include controllingmeans for controlling the illuminating means so that an extended area isfully recorded prior to recording in an area other than the extendedarea in a recordable area in a first data storage layer of the opticalstorage medium.

In addition, an optical read/write method of the present invention isarranged to include the steps of preparing an optical storage medium andfully recording an extended area prior to recording in an area otherthan the extended area in a recordable area in a first data storagelayer of the optical storage medium.

According to the arrangement, since an optical storage medium is usedwhich has an extended area in a recordable area of a first data storagelayer, as mentioned earlier, light can be projected at uniform intensityon substantially all recordable areas of the second data storage layer.Therefore, desirable read/write characteristics can be imparted withoutusing a complex read/write system.

In addition, the area other than the extended area in the recordablearea of the first data storage layer is as large as a recordable area ina second data storage layer. The position of the illuminating meansrelative to the optical storage medium can be controlled in the samemanner with respect to read/write in the area other than the extendedarea in the recordable area of the first data storage layer and withrespect to read/write in the recordable area of the second data storagelayer.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium and is arranged so as to include:identification information storing means for storing identificationinformation which is unique to the optical read/write apparatus and bywhich the optical read/write apparatus is distinguished from otheroptical read/write apparatuses; and controlling means for controllingthe illuminating means so that the optical storage medium holds theidentification information in an extended area.

In addition, an optical read/write method of the present invention isarranged to include the steps of preparing the optical storage mediumand storing in an extended area identification information which isunique to an individual optical read/write apparatus capable ofreading/writing on the optical storage medium and by which the opticalread/write apparatus is distinguished from other optical read/writeapparatuses.

According to the arrangement, an optical storage medium can store in itsextended area identification information by which the optical read/writeapparatus having read or written the storage medium can bedistinguished. Therefore, if in reading/writing an optical storagemedium, for example, the optical read/write apparatus first reads theidentification information from the extended area, and only when theidentification information readout matches the identificationinformation assigned to the apparatus, is allowed to read or read orwrite the medium, the illegal copying and other uses of the opticalstorage medium can be prevented.

The optical read/write apparatus may be arranged so that checking meansfor checking whether the identification information retrieved from theextended area of the optical storage medium matches the identificationinformation of the optical read/write apparatus stored in theidentification information storing means, wherein the controlling meanscontrols the illuminating means in reproducing data from the opticalstorage medium so as to read identification information stored in theextended area of the optical storage medium, and only when the checkingmeans determines that the two sets of identification information match,allows data to be read from the recordable area other than the extendedarea of any data storage layer.

The optical read/write method may be arranged so as to include the stepsof, in reproducing data from the optical storage medium, reading theidentification information from the extended area of the optical storagemedium, checking whether the identification information retrieved fromthe extended area matches the identification information of the opticalread/write apparatus, and only when the two sets of identificationinformation match each other as a result of the checking, starts data tobe read from the recordable area other than the extended area of anydata storage layer.

According to the arrangement, in reading data from the optical storagemedium, the optical read/write apparatus first reads the identificationinformation from the extended area of the optical storage medium andonly when the identification information readout and the identificationinformation assigned to the apparatus, allows data to be read from theoptical storage medium. The illegal copying and other uses of theoptical storage medium can be surely prevented.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium and is arranged so as to include: encryptioninformation storing means for storing encryption information by whichdata is encrypted before being recorded on the optical storage medium;and controlling means for controlling the illuminating means so that theoptical storage medium holds the encryption information in the extendedarea.

An optical read/write method of the present invention is arranged toinclude the steps of: preparing the optical storage medium; preparingencryption information by which data is encrypted before being stored inthe optical storage medium; and storing the encryption information inthe extended area.

According to the arrangement, the extended area of the optical storagemedium can hold encryption information by which data is encrypted beforebeing stored in the optical storage medium. Therefore, if when theoptical read/write apparatus records information on the optical storagemedium, encryption information is read out from the extended area andinformation is encrypted based on the encryption information beforebeing stored on the optical storage medium, it is only the opticalread/write apparatus which can decrypt the encryption information thatcan decrypt the information read out from the optical storage medium.Therefore, the illegal copying and other uses of the optical storagemedium can be prevented.

The optical read/write apparatus may be arranged so as to furtherinclude encrypting means for encrypting data recorded on the opticalstorage medium in reference to encryption information in the extendedarea, wherein the controlling means controls the illuminating means sothat recording information encrypted by the encrypting means is storedin the data storage layer.

The optical read/write method may be arranged so as to further includethe steps of encrypting data to be recorded on the optical storagemedium in reference to the encryption information in the extended areaand recording the encrypted recording information in the data storagelayer.

According to the arrangement, based on the encryption information storedin the extended area of the optical storage medium, information to berecorded on the optical storage medium is encrypted before beingrecorded on the optical storage medium.

The optical read/write apparatus may be further arranged so that thecontrolling means allows reproduction of only the recording informationwhich is encrypted based on the same encryption information as theencryption information stored in the encryption information storingmeans.

The optical read/write method may be further arranged so that only therecording information encrypted based on the same encryption informationas the encryption information prepared in advance.

According to the arrangement, only the information can be reproducedwhich is encrypted using the same encryption information as theencryption information assigned to the optical read/write apparatus.Thus, the illegal copying and other uses of the optical storage mediumcan be prevented if optical read/write apparatuses other than theoptical read/write apparatus provided with the encryption informationare used.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium and is arranged so as to include controllingmeans for controlling the illuminating means so as to test write data inthe extended area.

An optical read/write method of the present invention is arranged toinclude the steps of preparing the optical storage medium, and testwriting data in the extended area.

According to the arrangement, the extended area can be utilized as atest write area to determine the most suitable light beam intensity in,for example, writing on the optical storage medium. This eliminates theneed to provide a separate test write area in the recordable area otherthan the extended area of the optical storage medium and allows for moreefficient use of the recordable area of the optical storage medium.

The optical storage medium may be arranged so that the extended areaconstitutes a fully prerecorded pseudo-recording area.

According to the arrangement, the pseudo-recording area provides thefunctions of the extended area. Further, the recordable area other thanthe pseudo-recording area of the first data storage layer is as large asthe recordable area of the second data storage layer, and the positionof the illuminating means relative to the optical storage medium can becontrolled in the same manner with respect to read/write in therecordable area of the first data storage layer and with respect toread/write in the recordable area of the second data storage layer.

The optical storage medium may be arranged so that the pseudo-recordingarea stores identification information which is unique to an individualoptical storage medium and by which the optical storage medium isdistinguished from other optical storage media.

According to the arrangement,

in reading or writing data on the optical storage medium using anoptical read/write apparatus, the optical storage medium isreadable/writeable only with the optical read/write apparatus whichmatches the identification information. Thus, the illegal copying andother uses of the optical storage medium can be prevented.

The optical storage medium may be arranged so that the pseudo-recordingarea stores encryption information to encrypt information to be storedon the optical storage medium.

According to the arrangement, when the optical read/write apparatusrecords information on the optical storage medium, the opticalread/write apparatus first reads the encryption information from thepseudo-recording area, encrypts the information based on the encryptioninformation before the information is stored on the optical storagemedium; thus, it is only the optical read/write apparatus that candecrypt the encryption information that can decrypt the information readout from the optical storage medium. Therefore, the illegal copying andother uses of the optical storage medium can be prevented.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium, and is arranged so as to include: encryptingmeans for encrypt data recorded on the optical storage medium inreference to the encryption information in the pseudo-recording area;and controlling means for controlling the illuminating means so that therecording information encrypted by the encrypting means is recorded inthe data storage layer.

An optical read/write method of the present invention is arranged toinclude the steps of preparing the optical storage medium; encryptingdata recorded on the optical storage medium in reference to theencryption information in the pseudo-recording area; and recording theencrypted recording information in the data storage layer.

According to the arrangement information can be encrypted based on theencryption information recorded in the pseudo-recording area of theoptical storage medium before being recorded on the optical storagemedium.

The optical storage medium may be arranged so that the pseudo-recordingarea is not rewriteable.

According to the arrangement, the identification information and theencryption information stored in the optical storage medium

pseudo-recording area can be protected. The illegal copying and otheruses of the optical storage medium is better prevented.

In addition, as described earlier, in the present invention, in anarrangement whereby: a lumped address scheme is used, multiple datastorage layers are readable/writeable using a light incident to only oneside; and the optical transmittance varies due to the recording usingincident light, attempts are made to achieve desirable read/writecharacteristics.

To this end, for example, the optical disk 101 includes stacked datastorage layers each of which is readable/writeable separately from theother data storage layers and each data storage layer has an addressarea 104 in which address pits 112 are collectively formed. The seconddata storage layer of the optical disk 101 is readable/writeable usinglight transmitted through the first data storage layer. The address area104 of the first data storage layer has a continuous storage area 114where the transmittance has varied and a non-recorded area where thetransmittance has not varied. Thus, the quantity of light transmittedthrough the address area 104 is made closer to the quantity of lighttransmitted through the non-address area 105.

An optical storage medium of the present invention includes stackedmultiple data storage layer each of which is readable/writeableseparately from the other data storage layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having address tracks and at least one address area wherethere are collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the incidentlight, and is arranged so that one of every adjacent two of the addresstracks in the address area of a first data storage layer is continuouslyrecorded by means of the incident light, and the other is unrecorded,the first data storage layer being one of the data storage layers whichis located closest to a light-striking surface of the optical storagemedium, a second data storage layer being another of the data storagelayers which is located next to the first data storage layer, oppositethe light-striking surface.

In addition, an optical read/write apparatus of the present inventioncauses a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including multiple stacked datastorage layers each of which is readable/writeable separately from theother data storage layers by means of only a light beam striking oneside of the optical storage medium, each of the data storage layershaving multiple address tracks and at least one address area where thereare collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so that the optical read/write apparatus includescontrolling means for controlling the illuminating means so that one ofevery adjacent two of the address tracks in the address area of a firstdata storage layer is continuously recorded by means of the incidentlight, and the other one is unrecorded, the first data storage layerbeing one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer; opposite the light-striking surface.

In addition, an optical read/write method of the present inventionincludes the step of causing a read/write light beam to strike only oneside of an optical storage medium including multiple stacked datastorage layers each of which is readable/writeable separately from theother data storage layers by means of only a light beam striking oneside of the optical storage medium, each of the data storage layershaving multiple address tracks and at least one address area where thereare collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so as to further include the step of continuouslyrecording one of every adjacent two of the address tracks in the addressarea of a first data storage layer by means of the incident light, whileleaving the other one unrecorded, the first data storage layer being oneof the data storage layers which is located closest to a light-strikingsurface of the medium, a second data storage layer being another of thedata storage layers which is located next to the first data storagelayer, opposite the light-striking surface.

According to the arrangement, one of every adjacent two of the addresstracks in the address area of the first data storage layer located closeto the light-striking surface of the optical storage medium iscontinuously recorded by means of the incident light, and the other isunrecorded. Therefore, in reading/writing in the second data storagelayer, in a case where the light projected to focus on the second datastorage layer forms a light spot on the first data storage layer, therecorded area encompassed in the light spot of a non-address area in therecordable area of the first data storage layer, for example, the sum ofthe areas of the recording marks, is substantially equal to the sum ofthe continuously recorded areas encompassed in the light spot in theaddress area of the first data storage layer.

Thus, the intensity of light projected on the second data storage layerafter passing through the address area of the first data storage layerof the optical storage medium can be made substantially equal to theintensity of light projected on the second data storage layer afterpassing through the non-address area in the recordable area of the firstdata storage layer. As a result, read/write operations on the seconddata storage layer become more stable and desirable.

In addition, if the address area of the first data storage layer of theoptical storage medium is continuously recorded using the opticalread/write apparatus of the present invention or the optical read/writemethod in the aforementioned manner, the cost of the optical disk can bereduced by reducing the manufacturing steps of the optical disk.

The optical read/write apparatus may be arranged so that the controllingmeans, after reproducing the address information, controls theilluminating means based on the obtained address information so that oneof every adjacent two of the address tracks is continuously recorded andthe other one is unrecorded.

The optical read/write method may be arranged so that after reproducingthe address information, one of every adjacent two of the address tracksis continuously recorded and the other one is unrecorded, based on theobtained address information.

According to the arrangement, one of every adjacent two of the addresstracks is continuously recorded and the other one is unrecorded, basedon the address information derived from the address area. Therefore, theoptical storage medium does not require a particular arrangement todetermine whether the address track is to be continuously recorded orunrecorded.

An optical storage medium of the present invention includes multiplestacked data storage layers each of which is readable/writeableseparately from the other data storage layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having address tracks and at least one address area wherethere are collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so that each of the address tracks in the addressarea of a first data storage layer has a judgement mark to show whetherthe address track is to be continuously recorded or left unrecorded, thefirst data storage layer being one of the data storage layers which islocated closest to a light-striking surface of the medium, a second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface.

In addition, an optical read/write apparatus of the present inventioncauses a read/write light beam from illuminating means to strike onlyone side of the optical storage medium, and is arranged so as to includecontrolling means for determining based on information reproduced fromthe judgement mark whether each of the address tracks in the addressarea is to be continuously recorded or left unrecorded and controllingthe illuminating means according to a result of the determination sothat each of the address tracks is to be either continuously recorded orleft unrecorded.

In addition, an optical read/write method of the present inventionincludes the step of causing a read/write light beam to strike only oneside of the optical storage medium, and is arranged so as to furtherinclude the steps of determining based on information reproduced fromthe judgement mark whether each of the address tracks in the addressarea is to be continuously recorded or left unrecorded and controllingaccording to a result of the determination so that each of the addresstracks is to be continuously recorded by means of the incident light orleft unrecorded.

According to the arrangement, each of the address tracks in the addressarea of the first data storage layer located on the light-striking sideof the optical storage medium has a judgement mark showing whether theaddress track should be continuously recorded or left unrecorded. Theoptical read/write apparatus in which the optical storage medium isloaded can readily form based on the judgement mark a continuouslyrecorded area in an address area of the first data storage layer of theoptical storage medium.

In addition, the optical read/write apparatus can immediately determinebased on the judgement mark whether to continuously record the addresstrack and therefore quickly complete the process to continuously recordthe address track in the address area.

In addition, the judgement mark is specified to change into thefollowing state, provided that an area in a non-address area iscontinuously recorded based on an instruction from the judgement mark.That is, the judgement mark is specified so that in reading/writing inthe second data storage layer, in a case where the light projected tofocus on the second data storage layer forms a light spot on the firstdata storage layer, the recorded area encompassed in the light spot of anon-address area in the recordable area of the first data storage layer,for example, the sum of the areas of the recording marks, issubstantially equal to the sum of the continuously recorded areasencompassed in the light spot in the address area of the first datastorage layer. To this end, the judgement mark shows that, for example,one of every adjacent two of the address tracks in, for example, thefirst data storage layer is continuously recorded and the other one isleft unrecorded. As a result, using the optical storage medium of thepresent invention, read/write operations on the second data storagelayer become more stable and desirable.

In addition, according to the optical read/write apparatus of thepresent invention or the optical read/write method, the process ofcontinuously recording the address area of the first data storage layerof the optical storage medium can be implemented after the shipment ofthe optical storage medium in the aforementioned manner, and the cost ofthe optical storage medium can be reduced by reducing the manufacturingsteps of the optical storage medium.

An optical storage medium of the present invention includes multiplestacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother data storage layers by means of only a light beam striking oneside of the optical storage medium, each of the data storage layershaving multiple address tracks and at least one address area where thereare collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so that: among the address tracks in the addressarea of a first data storage layer, either those address tracks whichextend from the land or those address tracks which extend from thegroove are continuously recorded by means of the incident light, and theothers are unrecorded, the first data storage layer being one of thedata storage layers which is located closest to a light-striking surfaceof the medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

In addition, an optical read/write apparatus of the present inventioncausing a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including multiple stacked datastorage layers each of which is readable/writeable on both a land and agroove formed on the data storage layer separately from the other datastorage layer by means of a light beam striking one side of the opticalstorage medium, each of the data storage layers having multiple addresstracks and at least one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, and is arranged toinclude controlling means for controlling the illuminating means so thatin the address area of a first data storage layer, either those addresstracks which extend from the land or those which extend from the grooveare continuously recorded by means of the incident light, and the othersare unrecorded, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

In addition, an optical read/write method of the present inventionincludes the step of causing a read/write light beam to strike only oneside of an optical storage medium including multiple stacked datastorage layers each of which is readable/writeable on both a land and agroove formed on the data storage layer separately from the other datastorage layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having multipleaddress tracks and at least one address area where there arecollectively formed address information portions representing addressinformation, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so that in the address area of a first datastorage layer, either those address tracks which extend from the land orthose which extend from the groove are continuously recorded

by means of the incident light, and there others are unrecorded, thefirst data storage layer being one of the data storage layers which islocated closest to a light-striking surface of the medium, a second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface.

According to the arrangement, in the address area of the first datastorage layer on the light-striking side, either those address trackswhich extend from the land or those which extend from the groove arecontinuously recorded when data is written by means of incident light,and the others are left unrecorded. Therefore, in reading/writing on thesecond data storage layer, in a case where the light projected to focuson the second data storage layer forms a light spot on the first datastorage layer, the recorded area encompassed in the light spot of anon-address area in the recordable area of the first data storage layer,for example, the sum of the areas of the recording marks, issubstantially equal to the sum of the continuously recorded areasencompassed in the light spot in the address area of the first datastorage layer.

Thus, the intensity of light transmitted through the address area of thefirst data storage layer before reaching the second data storage layercan be made substantially equal to the intensity of light transmittedthrough the non-address area in the recordable area of the first datastorage layer before reaching the second data storage layer. As aresult, read/write operations on the second data storage layer becomemore stable and desirable.

An optical storage medium of the present invention includes multiplestacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother data storage layers by means of only a light beam striking oneside of the optical storage medium, each of the data storage layershaving multiple address tracks and at least one address area where thereare collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance when data is written by means of the light beam, and isarranged so that: in a first data storage layer, the address area has afirst address area and a second address area which are adjacent to eachother along tracks, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; the address information portions ineither the first and second address areas are formed in those addresstracks which extend from the land, and the address information portionsin the other one of the first and second address areas are formed inthose address tracks which extend from the groove; and either an areawhere the address information portions are formed or an area where noaddress information portions are formed is continuously recorded.

In addition, an optical read/write apparatus of the present inventioncauses a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including multiple stacked datastorage layers each of which is readable/writeable on both a land and agroove formed on the data storage layer separately from the other datastorage layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having multipleaddress tracks and at least one address area where there arecollectively formed address information portions representing addressinformation, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so as to include controlling means for controllingthe illuminating means so that: in a first data storage layer, theaddress area has a first address area and a second address area whichare adjacent to each other along tracks, the first data storage layerbeing one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface; and when theaddress information portions in either one of the first and secondaddress areas are formed in those address tracks which extend from theland, and the address information portions in the other one of the firstand second address areas are formed in those address tracks which extendfrom the groove, either an area where the address information portionsare formed or an area where no address information portions are formedis continuously recorded in the first and second address areas.

In addition, an optical read/write method of the present inventioncomprises the step of causing a read/write light beam to strike only oneside of an optical storage medium including multiple stacked datastorage layers each of which is readable/writeable on both a land and agroove formed on the data storage layer by means of only a light beamstriking one side of the optical storage medium, each of data storagelayers having multiple address tracks and at least one address areawhere there are collectively formed address information portionsrepresenting address information, the optical storage medium exhibitingan optical transmittance which varies when data is written by means ofthe light beam, and is arranged so that: in a first data storage layer,the address area has a first address area and a second address areawhich are adjacent to each other along tracks, the first data storagelayer being one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface; and the methodfurther comprises the steps of, when the address information portions ineither one of the first and second address areas are formed in thoseaddress tracks which extend from the land, and the address informationportions in the other one of the first and second address areas areformed in those address tracks which extend from the groove,continuously recording either an area where the address informationportions are formed or an area where no address information portions areformed in the first and second address areas by means of the incidentlight.

According to the arrangement, the address area of the first data storagelayer located on the light-striking side of the optical storage mediumis made of a first address area and a second address area which areadjacent to each other along tracks; the address information portions ineither one of the first and second address areas are formed in thoseaddress tracks which extend from the land, and the address informationportions in the other one of the first and second address areas areformed in those address tracks which extend from the groove; and eitheran area where the address information portions are formed or an areawhere no address information portions are formed is continuouslyrecorded. Therefore, in reading/writing on the second data storagelayer, in a case where the light projected to focus on the second datastorage layer forms a light spot on the first data storage layer, therecorded area encompassed in the light spot of a non-address area in therecordable area of the first data storage layer, for example, the sum ofthe areas of the recording marks, is substantially equal to the sum ofthe continuously recorded areas encompassed in the light spot in theaddress area of the first data storage layer.

Thus, the intensity of light transmitted through the address area of thefirst data storage layer before reaching the second data storage layercan be made substantially equal to the intensity of light transmittedthrough the non-address area in the recordable area of the first datastorage layer before reaching the second data storage layer. As aresult, read/write operations on the second data storage layer becomemore stable and desirable.

In addition,

if the address area of the first data storage layer of the opticalstorage medium is continuously recorded using the optical read/writeapparatus of the present invention or the optical read/write method inthe aforementioned manner, the cost of the optical storage medium can bereduced by reducing the manufacturing steps of the optical storagemedium.

In addition, the present invention enables stable read/write ofinformation on an optical disk with two or more storage layers withoutbeing affected by prepit areas.

To this end, the optical disk 201 includes a first storage layer 215 anda second storage layer 213 an outer prepit area 206 b as a prepit areais provided outside the outer periphery the recordable area 203 b of thesecond storage layer 213. Predetermined information is stored in theouter prepit area 206 b in advance using pits. Prepit information isreproduced by transmitting a light beam 217 through a recordable area203 b of the first storage layer 215 where the optical transmittance ishigh due to recording to the full capacity and then focusing on theouter prepit area 206 b. The provision of the outer prepit area 206 b onthe second storage layer 213 enables data to be read from and write intothe second storage layer 213 without being affected by prepit areas.

An optical storage medium of the present invention is preferably suchthat each of the data storage layers except for the last data storagelayer has a pseudo-recording area at such a position that allows lightto be transmitted to the prepit area, the pseudo-recording area, whenfully prerecorded, exhibiting a higher optical transmittance than otherareas.

In this manner, a pseudo-recording area, when fully prerecorded,exhibiting a higher optical transmittance than other areas is providedat such a position that allows light to be transmitted to the prepitarea, the pseudo-recording area; therefore, the light striking thelight-striking side storage layer can reach the prepit area afterpassing through the pseudo-recording area of any data storage layer, butthe last data storage layer. Therefore, the intensity of thereproduction signal of the prepit information reproduced from prepitarea does not fall. Therefore, the amplitude of the reproduction signalof the prepit information can be made greater.

Another optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium, and is arranged so as to include: lowfrequency variation removing means for removing low frequency variationsfrom the reproduction signal obtained from the prepit area; and digitalconverting means for converting the reproduction signal from which thelow frequency variations are removed to a digital signal using theconstant voltage as a reference.

In addition, an optical read/write method of the present inventionincludes the step of causing a read/write light beam from illuminatingmeans to strike only one side of the optical storage medium, and isarranged so as to further include the steps of removing low frequencyvariations from the reproduction signal obtained from the prepit area;and converting the reproduction signal from which the low frequencyvariations are removed to a digital signal using a constant voltage as areference.

According to the apparatus and method, the reproduction signal obtainedfrom reading off the prepit area is rid of low frequency variations bylow frequency variation removing means. The reproduction signal, fromwhich low frequency variations are removed, has an envelope whose meanlevel is substantially constant. Thereafter, the reproduction signal isconverted to a digital signal by digital converting means using theconstant voltage as a reference. In this manner, the envelope comes tohave a substantially constant mean level, in converting a reproductionsignal to a digital signal, the constant voltage can be used as areference. Therefore, the digital conversion can be carried out withoutbeing affected by variations in amplitude of the reproduction signal.For example, as mentioned in the foregoing, incident light illuminatinga recorded part and a non-recorded part of the first storage layer isfocused on the second storage layer, a digital signal can be producedstably from the reproduction signal even if the intensity of thereproduction signal of the prepit information varies with the rotationof the optical storage medium. Therefore, the prepit information of thesecond storage layer of the optical storage medium can be stablyreproduced.

An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe storage medium having the pseudo-recording area, and is arranged soas to include: recording status checking means for checking whether thepseudo-recording area is fully recorded or not based on a reproductionsignal obtained from the pseudo-recording area; and pseudo-recordingmeans for fully recording data in the pseudo-recording area if thepseudo-recording area is not fully recorded.

In addition, an optical read/write method of the present inventionincludes the step of causing a read/write light beam from illuminatingmeans to strike only one side of the storage medium with thepseudo-recording area, and is arranged so as to further include thesteps of fully recording the pseudo-recording area so that thepseudo-recording area transmits light therethrough to the prepit area.

According to the apparatus and method, the recording status checkingmeans checks whether or not the pseudo-recording area is fully recorded.If the check turns out that the pseudo-recording area is not fullyrecorded, the pseudo-recording means fully recorded the pseudo-recordingarea. Thus, the pseudo-recording area of the optical storage medium isformed by the optical read/write apparatus, and there is no need to forma pseudo-recording area on the optical storage medium in advance beforeshipment. Therefore, the cost of the optical storage medium can bereduced.

Another optical storage medium of the present invention includes: onelight-striking side storage layer provided as a data storage layer on alight-striking side; and one or more opposite-side storage layersprovided as data storage layers opposite the light-striking side fromthe light-striking side storage layer, and is arranged so that: thelight-striking side storage layer has a prepit area which includespreformed pits representative of data: and an optically transparentrecordable area of the light-striking side storage layer is formed widerthan the optically transparent recordable areas of the opposite-sidestorage layers.

With the arrangement, the recordable areas of the opposite-side storagelayers are smaller than the recordable area on the light-striking side.Therefore, in a case where the prepit area is provided adjacent to therecordable area on the light-striking side storage layer, lighttransmitted through the prepit area does not enter the recordable areasof the opposite-side storage layers. In addition, since lighttransmitted near the border between the recordable area of thelight-striking side storage layer and the prepit area is focused on therecordable areas of the opposite-side storage layers, even if therecordable areas of the opposite-side storage layers are small asmentioned in the foregoing, the light can be transmitted only throughthe recordable area of the light-striking side storage layer and focusedon the recordable areas of the opposite-side storage layers. Therefore,data can be stably read from and written into the last data storagelayer without being affected by the prepit area.

Another optical storage medium of the present invention includes: onelight-striking side storage layer provided as a data storage layer on alight-striking side; and one or more opposite-side storage layersprovided as data storage layers opposite the light-striking side fromthe light-striking side storage layer, and is arranged so that: thelight-striking side storage layer has a prepit area which includespreformed pits representative of data; and the prepit area allowstransmission of light so that light reaches the opposite-side storagelayers, at a transmittance substantially equal to that of a recordablearea of the light-striking side storage layer.

With the arrangement, since the prepit area allows light to betransmitted at a transmittance substantially equal that as thetransmittance of the recordable area of the light-striking side storagelayer, the light passing through the recordable area and through theprepit area has substantially the same intensity. Therefore, data can beread from and written to the last data storage layer stably withoutbeing affected by the prepit area.

The storage medium in which the prepit area is provided in thelight-striking side storage layer is preferably such that the recordableareas of the data storage layers except for the last data storage layerwhich is most distanced from the light-striking side storage layerexhibit, when fully recorded, higher optical transmittances than otherareas.

With the arrangement, in projecting read/write light to the recordableareas of the data storage layers except for the last data storage layer,the recordable areas come to have higher optical transmittances thanother areas upon completion of recording. Therefore, keeping therecordable area fully recorded enables the light passing through therecordable areas to remain sufficiently intense until it reaches atarget data storage layer. Therefore, data can be stably read andwritten on an optical storage medium with multiple storage layers.

An optical read/write apparatus causing a read/write light beam fromilluminating means to strike only one side of the optical storage mediumincludes controlling means for controlling the illuminating means sothat the recordable area of the light-striking side storage layer isfully recorded before the recordable areas of the opposite-side storagelayers which are adjacent to the light-striking side storage layer isread/written.

In addition, an optical read/write method including the step of causinga read/write light beam from illuminating means to strike only one sideof the optical storage medium includes the steps of fully recording therecordable area of the light-striking side storage layer andsubsequently reading or writing in the recordable areas of theopposite-side storage layers which are adjacent to the light-strikingside storage layer.

In reading or writing on the optical storage medium using such anapparatus or method, the controlling means controls the illuminatingmeans so that the recordable area of the light-striking side storagelayer fully recorded before the recordable area of a targetopposite-side storage layer is read or written. Therefore, in reading orwriting the opposite-side storage layers, the light passing through thelight-striking side storage layer remains sufficiently intense until itreaches the opposite-side storage layers. Therefore, data can be stablyread and written on the optical storage medium.

An optical storage medium having the transparent prepit area ispreferably such that the prepit area, under such illumination to fullyrecord the prepit area substantially identically to the recordable area,exhibits a high optical transmittance substantially equal to that of therecordable area.

With such an arrangement, the prepit area, when fully recorded underillumination, comes to exhibit a similar optical transmittance to thatof the recordable area. Therefore, the light passing through therecordable area and through the prepit area has substantially the sameintensity. Therefore, data can be read from and written to the last datastorage layer stably.

With this optical storage medium, preferably, on a pit row of the pitsin the prepit area, there is formed a continuous, fully recorded storagearea with neither the pits nor intervening portions between the pitsleft unrecorded, so that a fully recorded portion occupies asubstantially equal area in a part where light is concentrated in therecordable area and in a part where light is concentrated in the prepitarea.

With the arrangement, light forms a beam spot in both the recordablearea and the prepit area as it strikes the recordable area and theprepit area of the light-striking side storage layer. The continuousstorage area is formed on the pit row so that the area of the recordedportion in a part where light is concentrated in the beam spot issubstantially equal between the recordable area and the prepit area.Therefore, light transmitted through the recordable area and the prepitarea has similar intensity. Therefore, data can be stably read from orwritten into the last data storage layer.

An optical read/write apparatus causing a read/write light beam fromilluminating means to strike only one side of the optical storage mediumof which the prepit area exhibits a high optical transmittance underillumination includes: continuous storage area checking means forchecking based on a signal reproduced from the prepit area whether ornot the prepit area has a continuous storage area where areas interposedbetween the pits are continuously and fully recorded as to a pit row ofthe pits; and continuous recording means for performing such recordingthat on the pit row in the prepit area where the continuous storage areais not present, there is formed the continuous storage area so that afully recorded portion occupies a substantially equal area in a partwhere light is concentrated in the recordable area and in a part wherelight is concentrated in the prepit area.

In addition, an optical read/write method including the step of causinga read/write light beam from illuminating means to strike only one sideof the optical storage medium further includes the step of performingsuch recording that on the pit row in the prepit area where thecontinuous storage area is not present, there is formed the continuousstorage area where areas interposed between the pits are continuouslyand fully recorded as to a pit row of the pits so that a fully recordedportion occupies a substantially equal area in a part where light isconcentrated in the recordable area and in a part where light isconcentrated in the prepit area.

With the apparatus and method, the continuous storage area checkingmeans checks whether there is a continuous storage area. If the checkturns out that there is a continuous storage area, the continuousrecording means performs recording to form a continuous storage area.Thus, the formation of a continuous storage area on the optical storagemedium using the optical read/write apparatus eliminates the need toform a continuous storage area on the optical storage medium in advancebefore shipment. Therefore, the cost of the optical storage medium canbe reduced.

The invention being thus described, it will be obvious that the same waymay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. An optical read apparatus, comprising: illumination means forsupplying a read light beam; optical storage medium mounting means forsupporting an optical storage medium such that said read light beam fromsaid illuminating means strikes only a light-striking side of saidoptical storage medium, said optical storage medium including stackeddata storage layers each of which is readable/writeable separately fromthe other layers by means of a light beam striking said light-strikingside of said optical storage medium, wherein: said optical storagemedium is structured and configured such that a recordable area of afirst data storage layer including at least one recordable extended areaportion is provided above a second data storage layer in a direction inwhich the first and second data storage layers are stacked, and said atleast one recordable extended area portion extends in a radial directionof said optical storage medium past an entire recordable area of thesecond data storage layer, and, further, wherein said first data storagelayer is located closest to said light-striking surface of said opticalstorage medium, and the second data storage layer is located next to thefirst data storage layer, away from said light-striking surface.
 2. Anoptical read method comprising the steps of: providing a read apparatuscomprising: illumination means for supplying a read light beam; opticalstorage medium mounting means for supporting an optical storage mediumsuch that said read light beam from said illuminating means strikes onlya light-striking side of said optical storage medium, said opticalstorage medium including stacked data storage layers each of which isreadable/writeable separately from the other layers by means of a lightbeam striking said light-striking side of said optical storage medium,wherein: said optical storage medium is structured and configured suchthat a recordable area of a first data storage layer including at leastone extended area portion is provided above a second data storage layerin a direction in which the first and second data storage layers arestacked, and said at least one recordable extended area portion extendsin a radial direction of said optical storage medium past an entirerecordable area of the second data storage layer, and, further, whereinsaid first data storage layer is located closest to said light-strikingsurface of said optical storage medium, and the second data storagelayer is located next to the first data storage layer, away from saidlight-striking surface; and reading data from at least one of thestacked data storage layers.